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 $86.42   8.818%   $94.0405   $94.04   $94.05   $94.00  
  Purchase #2 $28.28   8.202%   $30.5995   $30.60   $30.60   $30.60  
  Purchase #3 $245.41   4.209%   $255.7393   $255.74   $255.75   $255.70  
  Purchase #4 $68.53   11.628%   $76.4987   $76.50   $76.50   $76.50  
  Purchase #5 $169.28   7.629%   $182.1944   $182.19   $182.20   $182.20  
  Purchase #6 $51.56   12.140%   $57.8194   $57.82   $57.80   $57.80  
  Purchase #7 $140.48   7.317%   $150.7589   $150.76   $150.75   $150.80  
  7 purchase totals = $789.96       $847.6507   $847.65   $847.65   $847.60