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 $62.95   8.807%   $68.494   $68.49   $68.50   $68.50  
  Purchase #2 $190.49   5.641%   $201.2355   $201.24   $201.25   $201.20  
  Purchase #3 $104.35   13.450%   $118.3851   $118.39   $118.40   $118.40  
  Purchase #4 $17.96   11.577%   $20.0392   $20.04   $20.05   $20.00  
  Purchase #5 $78.49   10.815%   $86.9787   $86.98   $87.00   $87.00  
  Purchase #6 $188.84   9.130%   $206.0811   $206.08   $206.10   $206.10  
  Purchase #7 $146.60   11.520%   $163.4883   $163.49   $163.50   $163.50  
  7 purchase totals = $789.68       $864.7019   $864.71   $864.80   $864.70