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 $207.86   13.462%   $235.8421   $235.84   $235.85   $235.80  
  Purchase #2 $188.51   9.672%   $206.7427   $206.74   $206.75   $206.70  
  Purchase #3 $21.33   10.775%   $23.6283   $23.63   $23.65   $23.60  
  Purchase #4 $82.87   7.196%   $88.8333   $88.83   $88.85   $88.80  
  Purchase #5 $113.78   10.141%   $125.3184   $125.32   $125.30   $125.30  
  Purchase #6 $219.83   7.766%   $236.902   $236.90   $236.90   $236.90  
  Purchase #7 $228.72   8.685%   $248.5843   $248.58   $248.60   $248.60  
  7 purchase totals = $1,062.90       $1,165.8511   $1,165.84   $1,165.90   $1,165.70