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 $55.41   3.200%   $57.1831   $57.18   $57.20   $57.20  
  Purchase #2 $239.69   12.203%   $268.9394   $268.94   $268.95   $268.90  
  Purchase #3 $159.49   6.275%   $169.498   $169.50   $169.50   $169.50  
  Purchase #4 $175.78   12.243%   $197.3007   $197.30   $197.30   $197.30  
  Purchase #5 $139.78   10.301%   $154.1787   $154.18   $154.20   $154.20  
  Purchase #6 $223.30   9.107%   $243.6359   $243.64   $243.65   $243.60  
  Purchase #7 $13.37   13.354%   $15.1554   $15.16   $15.15   $15.20  
  7 purchase totals = $1,006.82       $1,105.8912   $1,105.90   $1,105.95   $1,105.90