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 $246.29   4.850%   $258.2351   $258.24   $258.25   $258.20  
  Purchase #2 $173.38   6.277%   $184.2631   $184.26   $184.25   $184.30  
  Purchase #3 $32.60   8.192%   $35.2706   $35.27   $35.25   $35.30  
  Purchase #4 $16.64   7.362%   $17.865   $17.87   $17.85   $17.90  
  Purchase #5 $101.78   10.234%   $112.1962   $112.20   $112.20   $112.20  
  Purchase #6 $135.64   10.725%   $150.1874   $150.19   $150.20   $150.20  
  Purchase #7 $204.61   6.347%   $217.5966   $217.60   $217.60   $217.60  
  7 purchase totals = $910.94       $975.6140   $975.63   $975.60   $975.70