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 $92.34   3.686%   $95.7437   $95.74   $95.75   $95.70  
  Purchase #2 $31.27   11.829%   $34.9689   $34.97   $34.95   $35.00  
  Purchase #3 $230.57   6.444%   $245.4279   $245.43   $245.45   $245.40  
  Purchase #4 $36.61   8.477%   $39.7134   $39.71   $39.70   $39.70  
  Purchase #5 $32.46   5.379%   $34.206   $34.21   $34.20   $34.20  
  Purchase #6 $129.96   3.408%   $134.389   $134.39   $134.40   $134.40  
  Purchase #7 $117.58   12.455%   $132.2246   $132.22   $132.20   $132.20  
  7 purchase totals = $670.79       $716.6735   $716.67   $716.65   $716.60