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 $48.82   13.398%   $55.3609   $55.36   $55.35   $55.40  
  Purchase #2 $126.89   10.546%   $140.2718   $140.27   $140.25   $140.30  
  Purchase #3 $63.36   5.718%   $66.9829   $66.98   $67.00   $67.00  
  Purchase #4 $166.56   10.872%   $184.6684   $184.67   $184.65   $184.70  
  Purchase #5 $230.91   8.308%   $250.094   $250.09   $250.10   $250.10  
  Purchase #6 $163.85   11.699%   $183.0188   $183.02   $183.00   $183.00  
  Purchase #7 $59.73   5.714%   $63.143   $63.14   $63.15   $63.10  
  7 purchase totals = $860.12       $943.5398   $943.53   $943.50   $943.60