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 $48.32   8.774%   $52.5596   $52.56   $52.55   $52.60  
  Purchase #2 $111.31   6.356%   $118.3849   $118.38   $118.40   $118.40  
  Purchase #3 $78.38   4.247%   $81.7088   $81.71   $81.70   $81.70  
  Purchase #4 $50.32   12.487%   $56.6035   $56.60   $56.60   $56.60  
  Purchase #5 $94.85   13.142%   $107.3152   $107.32   $107.30   $107.30  
  Purchase #6 $172.69   12.334%   $193.9896   $193.99   $194.00   $194.00  
  Purchase #7 $177.58   3.318%   $183.4721   $183.47   $183.45   $183.50  
  7 purchase totals = $733.45       $794.0337   $794.03   $794.00   $794.10