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 $182.32   13.412%   $206.7728   $206.77   $206.75   $206.80  
  Purchase #2 $112.41   10.189%   $123.8635   $123.86   $123.85   $123.90  
  Purchase #3 $146.96   13.476%   $166.7643   $166.76   $166.75   $166.80  
  Purchase #4 $48.44   4.613%   $50.6745   $50.67   $50.65   $50.70  
  Purchase #5 $44.77   3.118%   $46.1659   $46.17   $46.15   $46.20  
  Purchase #6 $131.50   5.478%   $138.7036   $138.70   $138.70   $138.70  
  Purchase #7 $187.55   13.762%   $213.3606   $213.36   $213.35   $213.40  
  7 purchase totals = $853.95       $946.3052   $946.29   $946.20   $946.50