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 $32.36   13.773%   $36.8169   $36.82   $36.80   $36.80  
  Purchase #2 $180.76   5.282%   $190.3077   $190.31   $190.30   $190.30  
  Purchase #3 $200.97   8.419%   $217.8897   $217.89   $217.90   $217.90  
  Purchase #4 $154.57   5.352%   $162.8426   $162.84   $162.85   $162.80  
  Purchase #5 $79.57   10.874%   $88.2224   $88.22   $88.20   $88.20  
  Purchase #6 $118.65   6.193%   $125.998   $126.00   $126.00   $126.00  
  Purchase #7 $12.54   13.812%   $14.272   $14.27   $14.25   $14.30  
  7 purchase totals = $779.42       $836.3493   $836.35   $836.30   $836.30