Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $206.31   9.371%   $225.6433   $225.64   $225.65   $225.60  
  Purchase #2 $223.49   7.638%   $240.5602   $240.56   $240.55   $240.60  
  Purchase #3 $232.35   11.183%   $258.3337   $258.33   $258.35   $258.30  
  Purchase #4 $118.78   6.335%   $126.3047   $126.30   $126.30   $126.30  
  Purchase #5 $192.43   5.489%   $202.9925   $202.99   $203.00   $203.00  
  Purchase #6 $202.71   3.145%   $209.0852   $209.09   $209.10   $209.10  
  Purchase #7 $157.66   10.155%   $173.6704   $173.67   $173.65   $173.70  
  7 purchase totals = $1,333.73       $1,436.5900   $1,436.58   $1,436.60   $1,436.60