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 $49.73   8.543%   $53.9784   $53.98   $54.00   $54.00  
  Purchase #2 $191.98   7.197%   $205.7968   $205.80   $205.80   $205.80  
  Purchase #3 $46.43   3.252%   $47.9399   $47.94   $47.95   $47.90  
  Purchase #4 $78.65   5.417%   $82.9105   $82.91   $82.90   $82.90  
  Purchase #5 $149.77   13.407%   $169.8497   $169.85   $169.85   $169.80  
  Purchase #6 $107.79   11.411%   $120.0899   $120.09   $120.10   $120.10  
  Purchase #7 $102.65   11.348%   $114.2987   $114.30   $114.30   $114.30  
  7 purchase totals = $727.00       $794.8639   $794.87   $794.90   $794.80