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 $67.34   11.633%   $75.1737   $75.17   $75.15   $75.20  
  Purchase #2 $248.76   9.382%   $272.0987   $272.10   $272.10   $272.10  
  Purchase #3 $46.74   4.277%   $48.7391   $48.74   $48.75   $48.70  
  Purchase #4 $32.69   7.560%   $35.1614   $35.16   $35.15   $35.20  
  Purchase #5 $189.93   7.314%   $203.8215   $203.82   $203.80   $203.80  
  Purchase #6 $68.92   5.463%   $72.6851   $72.69   $72.70   $72.70  
  Purchase #7 $237.97   12.157%   $266.9   $266.90   $266.90   $266.90  
  7 purchase totals = $892.35       $974.5795   $974.58   $974.55   $974.60