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 $83.66   12.707%   $94.2907   $94.29   $94.30   $94.30  
  Purchase #2 $84.63   5.238%   $89.0629   $89.06   $89.05   $89.10  
  Purchase #3 $42.41   8.369%   $45.9593   $45.96   $45.95   $46.00  
  Purchase #4 $72.31   3.804%   $75.0607   $75.06   $75.05   $75.10  
  Purchase #5 $126.37   5.452%   $133.2597   $133.26   $133.25   $133.30  
  Purchase #6 $100.73   13.184%   $114.0102   $114.01   $114.00   $114.00  
  Purchase #7 $70.62   4.767%   $73.9865   $73.99   $74.00   $74.00  
  7 purchase totals = $580.73       $625.6300   $625.63   $625.60   $625.80