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 $58.57   11.667%   $65.4034   $65.40   $65.40   $65.40  
  Purchase #2 $44.68   11.194%   $49.6815   $49.68   $49.70   $49.70  
  Purchase #3 $241.62   7.172%   $258.949   $258.95   $258.95   $258.90  
  Purchase #4 $114.63   13.413%   $130.0053   $130.01   $130.00   $130.00  
  Purchase #5 $46.35   11.218%   $51.5495   $51.55   $51.55   $51.50  
  Purchase #6 $250.38   8.515%   $271.6999   $271.70   $271.70   $271.70  
  Purchase #7 $54.26   8.826%   $59.049   $59.05   $59.05   $59.00  
  7 purchase totals = $810.49       $886.3376   $886.34   $886.35   $886.20