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 $99.99   5.527%   $105.5164   $105.52   $105.50   $105.50  
  Purchase #2 $224.90   9.105%   $245.3771   $245.38   $245.40   $245.40  
  Purchase #3 $125.74   11.765%   $140.5333   $140.53   $140.55   $140.50  
  Purchase #4 $13.79   8.629%   $14.9799   $14.98   $15.00   $15.00  
  Purchase #5 $120.30   7.303%   $129.0855   $129.09   $129.10   $129.10  
  Purchase #6 $186.34   12.684%   $209.9754   $209.98   $210.00   $210.00  
  Purchase #7 $246.56   10.193%   $271.6919   $271.69   $271.70   $271.70  
  7 purchase totals = $1,017.62       $1,117.1595   $1,117.17   $1,117.25   $1,117.20