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 $88.55   11.595%   $98.8174   $98.82   $98.80   $98.80  
  Purchase #2 $236.60   9.361%   $258.7481   $258.75   $258.75   $258.70  
  Purchase #3 $144.54   4.676%   $151.2987   $151.30   $151.30   $151.30  
  Purchase #4 $83.77   10.819%   $92.8331   $92.83   $92.85   $92.80  
  Purchase #5 $97.56   5.598%   $103.0214   $103.02   $103.00   $103.00  
  Purchase #6 $55.90   12.758%   $63.0317   $63.03   $63.05   $63.00  
  Purchase #7 $24.27   3.828%   $25.1991   $25.20   $25.20   $25.20  
  7 purchase totals = $731.19       $792.9495   $792.95   $792.95   $792.80