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 $61.76   8.483%   $66.9991   $67.00   $67.00   $67.00  
  Purchase #2 $86.36   10.388%   $95.3311   $95.33   $95.35   $95.30  
  Purchase #3 $211.71   7.530%   $227.6518   $227.65   $227.65   $227.70  
  Purchase #4 $46.48   3.594%   $48.1505   $48.15   $48.15   $48.20  
  Purchase #5 $180.37   9.718%   $197.8984   $197.90   $197.90   $197.90  
  Purchase #6 $94.40   13.648%   $107.2837   $107.28   $107.30   $107.30  
  Purchase #7 $44.92   13.447%   $50.9604   $50.96   $50.95   $51.00  
  7 purchase totals = $726.00       $794.2750   $794.27   $794.30   $794.40