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 $195.56   11.786%   $218.6087   $218.61   $218.60   $218.60  
  Purchase #2 $237.68   12.865%   $268.2575   $268.26   $268.25   $268.30  
  Purchase #3 $77.38   9.464%   $84.7032   $84.70   $84.70   $84.70  
  Purchase #4 $12.34   11.842%   $13.8013   $13.80   $13.80   $13.80  
  Purchase #5 $49.75   6.610%   $53.0385   $53.04   $53.05   $53.00  
  Purchase #6 $46.40   6.268%   $49.3084   $49.31   $49.30   $49.30  
  Purchase #7 $229.32   6.491%   $244.2052   $244.21   $244.20   $244.20  
  7 purchase totals = $848.43       $931.9228   $931.93   $931.90   $931.90