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 $236.39   3.426%   $244.4887   $244.49   $244.50   $244.50  
  Purchase #2 $210.84   12.155%   $236.4676   $236.47   $236.45   $236.50  
  Purchase #3 $157.73   8.103%   $170.5109   $170.51   $170.50   $170.50  
  Purchase #4 $127.48   5.533%   $134.5335   $134.53   $134.55   $134.50  
  Purchase #5 $177.97   9.739%   $195.3025   $195.30   $195.30   $195.30  
  Purchase #6 $225.51   8.306%   $244.2409   $244.24   $244.25   $244.20  
  Purchase #7 $227.73   11.164%   $253.1538   $253.15   $253.15   $253.20  
  7 purchase totals = $1,363.65       $1,478.6979   $1,478.69   $1,478.70   $1,478.70