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 $241.73   5.469%   $254.9502   $254.95   $254.95   $255.00  
  Purchase #2 $205.76   11.491%   $229.4039   $229.40   $229.40   $229.40  
  Purchase #3 $248.30   5.118%   $261.008   $261.01   $261.00   $261.00  
  Purchase #4 $159.88   11.217%   $177.8137   $177.81   $177.80   $177.80  
  Purchase #5 $241.77   7.771%   $260.5579   $260.56   $260.55   $260.60  
  Purchase #6 $154.60   8.828%   $168.2481   $168.25   $168.25   $168.20  
  Purchase #7 $47.57   13.792%   $54.1309   $54.13   $54.15   $54.10  
  7 purchase totals = $1,299.61       $1,406.1127   $1,406.11   $1,406.10   $1,406.10