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 $62.47   5.589%   $65.9614   $65.96   $65.95   $66.00  
  Purchase #2 $120.33   9.803%   $132.1259   $132.13   $132.15   $132.10  
  Purchase #3 $158.81   11.826%   $177.5909   $177.59   $177.60   $177.60  
  Purchase #4 $50.57   9.424%   $55.3357   $55.34   $55.35   $55.30  
  Purchase #5 $46.53   4.719%   $48.7258   $48.73   $48.75   $48.70  
  Purchase #6 $227.84   11.846%   $254.8299   $254.83   $254.85   $254.80  
  Purchase #7 $207.82   6.872%   $222.1014   $222.10   $222.10   $222.10  
  7 purchase totals = $874.37       $956.6710   $956.68   $956.75   $956.60