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 $126.34   6.138%   $134.0947   $134.09   $134.10   $134.10  
  Purchase #2 $204.68   6.381%   $217.7406   $217.74   $217.75   $217.70  
  Purchase #3 $73.59   12.211%   $82.5761   $82.58   $82.60   $82.60  
  Purchase #4 $149.87   11.409%   $166.9687   $166.97   $166.95   $167.00  
  Purchase #5 $189.96   12.505%   $213.7145   $213.71   $213.70   $213.70  
  Purchase #6 $188.27   3.766%   $195.3602   $195.36   $195.35   $195.40  
  Purchase #7 $61.79   12.400%   $69.452   $69.45   $69.45   $69.50  
  7 purchase totals = $994.50       $1,079.9068   $1,079.90   $1,079.90   $1,080.00