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 $29.89   12.172%   $33.5282   $33.53   $33.55   $33.50  
  Purchase #2 $98.34   5.718%   $103.9631   $103.96   $103.95   $104.00  
  Purchase #3 $122.49   3.378%   $126.6277   $126.63   $126.65   $126.60  
  Purchase #4 $103.83   9.870%   $114.078   $114.08   $114.10   $114.10  
  Purchase #5 $97.62   6.198%   $103.6705   $103.67   $103.65   $103.70  
  Purchase #6 $244.67   9.863%   $268.8018   $268.80   $268.80   $268.80  
  Purchase #7 $195.71   9.492%   $214.2868   $214.29   $214.30   $214.30  
  7 purchase totals = $892.55       $964.9561   $964.96   $965.00   $965.00