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 $56.62   12.413%   $63.6482   $63.65   $63.65   $63.60  
  Purchase #2 $154.54   9.377%   $169.0312   $169.03   $169.05   $169.00  
  Purchase #3 $95.95   9.594%   $105.1554   $105.16   $105.15   $105.20  
  Purchase #4 $96.81   13.382%   $109.7651   $109.77   $109.75   $109.80  
  Purchase #5 $193.36   8.847%   $210.4666   $210.47   $210.45   $210.50  
  Purchase #6 $63.97   5.148%   $67.2632   $67.26   $67.25   $67.30  
  Purchase #7 $172.41   11.872%   $192.8785   $192.88   $192.90   $192.90  
  7 purchase totals = $833.66       $918.2082   $918.22   $918.20   $918.30