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 $113.58   11.215%   $126.318   $126.32   $126.30   $126.30  
  Purchase #2 $93.38   6.680%   $99.6178   $99.62   $99.60   $99.60  
  Purchase #3 $148.44   9.751%   $162.9144   $162.91   $162.90   $162.90  
  Purchase #4 $138.67   11.358%   $154.4201   $154.42   $154.40   $154.40  
  Purchase #5 $21.86   10.312%   $24.1142   $24.11   $24.10   $24.10  
  Purchase #6 $67.76   10.856%   $75.116   $75.12   $75.10   $75.10  
  Purchase #7 $225.50   7.728%   $242.9266   $242.93   $242.95   $242.90  
  7 purchase totals = $809.19       $885.4271   $885.43   $885.35   $885.30