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 $8.96   8.581%   $9.7289   $9.73   $9.75   $9.70  
  Purchase #2 $114.86   6.114%   $121.8825   $121.88   $121.90   $121.90  
  Purchase #3 $47.54   7.240%   $50.9819   $50.98   $51.00   $51.00  
  Purchase #4 $85.42   13.237%   $96.727   $96.73   $96.75   $96.70  
  Purchase #5 $166.68   11.462%   $185.7849   $185.78   $185.80   $185.80  
  Purchase #6 $56.84   6.220%   $60.3754   $60.38   $60.40   $60.40  
  Purchase #7 $92.61   6.319%   $98.462   $98.46   $98.45   $98.50  
  7 purchase totals = $572.91       $623.9426   $623.94   $624.05   $624.00