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 $60.69   10.643%   $67.1492   $67.15   $67.15   $67.10  
  Purchase #2 $182.41   12.841%   $205.8333   $205.83   $205.85   $205.80  
  Purchase #3 $59.66   4.604%   $62.4067   $62.41   $62.40   $62.40  
  Purchase #4 $141.78   10.704%   $156.9561   $156.96   $156.95   $157.00  
  Purchase #5 $94.80   13.741%   $107.8265   $107.83   $107.85   $107.80  
  Purchase #6 $104.82   12.767%   $118.2024   $118.20   $118.20   $118.20  
  Purchase #7 $90.68   13.517%   $102.9372   $102.94   $102.95   $102.90  
  7 purchase totals = $734.84       $821.3114   $821.32   $821.35   $821.20