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 $246.46   6.202%   $261.7454   $261.75   $261.75   $261.70  
  Purchase #2 $234.35   3.713%   $243.0514   $243.05   $243.05   $243.10  
  Purchase #3 $156.51   6.274%   $166.3294   $166.33   $166.35   $166.30  
  Purchase #4 $240.88   4.421%   $251.5293   $251.53   $251.55   $251.50  
  Purchase #5 $34.91   8.709%   $37.9503   $37.95   $37.95   $38.00  
  Purchase #6 $134.75   6.467%   $143.4643   $143.46   $143.45   $143.50  
  Purchase #7 $178.48   8.831%   $194.2416   $194.24   $194.25   $194.20  
  7 purchase totals = $1,226.34       $1,298.3117   $1,298.31   $1,298.35   $1,298.30