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 $28.95   10.554%   $32.0054   $32.01   $32.00   $32.00  
  Purchase #2 $47.33   9.380%   $51.7696   $51.77   $51.75   $51.80  
  Purchase #3 $244.84   4.864%   $256.749   $256.75   $256.75   $256.70  
  Purchase #4 $84.71   10.345%   $93.4732   $93.47   $93.45   $93.50  
  Purchase #5 $5.41   3.844%   $5.618   $5.62   $5.60   $5.60  
  Purchase #6 $247.37   6.353%   $263.0854   $263.09   $263.10   $263.10  
  Purchase #7 $15.96   13.139%   $18.057   $18.06   $18.05   $18.10  
  7 purchase totals = $674.57       $720.7576   $720.77   $720.70   $720.80