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 $201.86   6.764%   $215.5138   $215.51   $215.50   $215.50  
  Purchase #2 $69.60   8.440%   $75.4742   $75.47   $75.45   $75.50  
  Purchase #3 $195.31   11.321%   $217.421   $217.42   $217.40   $217.40  
  Purchase #4 $151.33   11.766%   $169.1355   $169.14   $169.15   $169.10  
  Purchase #5 $59.45   6.190%   $63.13   $63.13   $63.15   $63.10  
  Purchase #6 $95.98   11.808%   $107.3133   $107.31   $107.30   $107.30  
  Purchase #7 $56.53   13.760%   $64.3085   $64.31   $64.30   $64.30  
  7 purchase totals = $830.06       $912.2963   $912.29   $912.25   $912.20