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 $66.30   13.541%   $75.2777   $75.28   $75.30   $75.30  
  Purchase #2 $96.65   8.733%   $105.0904   $105.09   $105.10   $105.10  
  Purchase #3 $119.78   10.793%   $132.7079   $132.71   $132.70   $132.70  
  Purchase #4 $194.86   6.708%   $207.9312   $207.93   $207.95   $207.90  
  Purchase #5 $72.63   11.497%   $80.9803   $80.98   $81.00   $81.00  
  Purchase #6 $23.44   6.728%   $25.017   $25.02   $25.00   $25.00  
  Purchase #7 $24.60   7.723%   $26.4999   $26.50   $26.50   $26.50  
  7 purchase totals = $598.26       $653.5044   $653.51   $653.55   $653.50