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 $194.93   13.266%   $220.7894   $220.79   $220.80   $220.80  
  Purchase #2 $249.35   5.131%   $262.1441   $262.14   $262.15   $262.10  
  Purchase #3 $126.87   13.427%   $143.9048   $143.90   $143.90   $143.90  
  Purchase #4 $149.47   12.193%   $167.6949   $167.69   $167.70   $167.70  
  Purchase #5 $12.33   6.361%   $13.1143   $13.11   $13.10   $13.10  
  Purchase #6 $5.93   8.122%   $6.4116   $6.41   $6.40   $6.40  
  Purchase #7 $101.58   10.527%   $112.2733   $112.27   $112.25   $112.30  
  7 purchase totals = $840.46       $926.3324   $926.31   $926.30   $926.30