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 $237.35   6.528%   $252.8442   $252.84   $252.85   $252.80  
  Purchase #2 $114.37   9.437%   $125.1631   $125.16   $125.15   $125.20  
  Purchase #3 $119.63   11.372%   $133.2343   $133.23   $133.25   $133.20  
  Purchase #4 $31.73   9.565%   $34.765   $34.77   $34.75   $34.80  
  Purchase #5 $161.33   5.546%   $170.2774   $170.28   $170.30   $170.30  
  Purchase #6 $214.89   7.600%   $231.2216   $231.22   $231.20   $231.20  
  Purchase #7 $72.98   4.439%   $76.2196   $76.22   $76.20   $76.20  
  7 purchase totals = $952.28       $1,023.7252   $1,023.72   $1,023.70   $1,023.70