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 $54.54   9.156%   $59.5337   $59.53   $59.55   $59.50  
  Purchase #2 $119.97   5.497%   $126.5648   $126.56   $126.55   $126.60  
  Purchase #3 $112.50   10.467%   $124.2754   $124.28   $124.30   $124.30  
  Purchase #4 $232.96   6.688%   $248.5404   $248.54   $248.55   $248.50  
  Purchase #5 $134.61   8.532%   $146.0949   $146.09   $146.10   $146.10  
  Purchase #6 $18.85   9.357%   $20.6138   $20.61   $20.60   $20.60  
  Purchase #7 $20.75   12.777%   $23.4012   $23.40   $23.40   $23.40  
  7 purchase totals = $694.18       $749.0242   $749.01   $749.05   $749.00