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 $236.27   7.194%   $253.2673   $253.27   $253.25   $253.30  
  Purchase #2 $242.39   6.494%   $258.1308   $258.13   $258.15   $258.10  
  Purchase #3 $82.93   12.388%   $93.2034   $93.20   $93.20   $93.20  
  Purchase #4 $141.73   11.294%   $157.737   $157.74   $157.75   $157.70  
  Purchase #5 $191.54   7.796%   $206.4725   $206.47   $206.45   $206.50  
  Purchase #6 $64.78   11.784%   $72.4137   $72.41   $72.40   $72.40  
  Purchase #7 $178.78   9.253%   $195.3225   $195.32   $195.30   $195.30  
  7 purchase totals = $1,138.42       $1,236.5472   $1,236.54   $1,236.50   $1,236.50