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 $62.48   10.162%   $68.8292   $68.83   $68.85   $68.80  
  Purchase #2 $183.95   5.646%   $194.3358   $194.34   $194.35   $194.30  
  Purchase #3 $150.71   12.334%   $169.2986   $169.30   $169.30   $169.30  
  Purchase #4 $16.97   5.342%   $17.8765   $17.88   $17.90   $17.90  
  Purchase #5 $151.86   8.413%   $164.636   $164.64   $164.65   $164.60  
  Purchase #6 $106.35   7.632%   $114.4666   $114.47   $114.45   $114.50  
  Purchase #7 $53.49   10.719%   $59.2236   $59.22   $59.20   $59.20  
  7 purchase totals = $725.81       $788.6663   $788.68   $788.70   $788.60