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 $204.99   4.772%   $214.7721   $214.77   $214.75   $214.80  
  Purchase #2 $87.73   8.735%   $95.3932   $95.39   $95.40   $95.40  
  Purchase #3 $114.79   6.218%   $121.9276   $121.93   $121.95   $121.90  
  Purchase #4 $108.40   4.404%   $113.1739   $113.17   $113.15   $113.20  
  Purchase #5 $167.33   4.559%   $174.9586   $174.96   $174.95   $175.00  
  Purchase #6 $44.39   4.784%   $46.5136   $46.51   $46.50   $46.50  
  Purchase #7 $101.53   12.500%   $114.2213   $114.22   $114.20   $114.20  
  7 purchase totals = $829.16       $880.9603   $880.95   $880.90   $881.00