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 $148.97   13.478%   $169.0482   $169.05   $169.05   $169.00  
  Purchase #2 $110.94   3.443%   $114.7597   $114.76   $114.75   $114.80  
  Purchase #3 $11.96   6.595%   $12.7488   $12.75   $12.75   $12.70  
  Purchase #4 $166.84   10.467%   $184.3031   $184.30   $184.30   $184.30  
  Purchase #5 $64.35   8.142%   $69.5894   $69.59   $69.60   $69.60  
  Purchase #6 $164.73   7.403%   $176.925   $176.93   $176.95   $176.90  
  Purchase #7 $210.93   12.340%   $236.9588   $236.96   $236.95   $237.00  
  7 purchase totals = $878.72       $964.3330   $964.34   $964.35   $964.30