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 $140.93   8.251%   $152.5581   $152.56   $152.55   $152.60  
  Purchase #2 $189.44   4.430%   $197.8322   $197.83   $197.85   $197.80  
  Purchase #3 $24.98   5.161%   $26.2692   $26.27   $26.25   $26.30  
  Purchase #4 $134.37   12.543%   $151.224   $151.22   $151.20   $151.20  
  Purchase #5 $163.42   11.549%   $182.2934   $182.29   $182.30   $182.30  
  Purchase #6 $138.62   11.378%   $154.3922   $154.39   $154.40   $154.40  
  Purchase #7 $89.72   13.253%   $101.6106   $101.61   $101.60   $101.60  
  7 purchase totals = $881.48       $966.1797   $966.17   $966.15   $966.20