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 $83.74   11.854%   $93.6665   $93.67   $93.65   $93.70  
  Purchase #2 $89.58   10.394%   $98.8909   $98.89   $98.90   $98.90  
  Purchase #3 $151.91   4.134%   $158.19   $158.19   $158.20   $158.20  
  Purchase #4 $213.50   5.488%   $225.2169   $225.22   $225.20   $225.20  
  Purchase #5 $28.71   13.384%   $32.5525   $32.55   $32.55   $32.60  
  Purchase #6 $155.79   9.437%   $170.4919   $170.49   $170.50   $170.50  
  Purchase #7 $13.48   5.863%   $14.2703   $14.27   $14.25   $14.30  
  7 purchase totals = $736.71       $793.2790   $793.28   $793.25   $793.40