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 $88.89   4.666%   $93.0376   $93.04   $93.05   $93.00  
  Purchase #2 $45.99   3.115%   $47.4226   $47.42   $47.40   $47.40  
  Purchase #3 $15.65   4.435%   $16.3441   $16.34   $16.35   $16.30  
  Purchase #4 $131.91   12.726%   $148.6969   $148.70   $148.70   $148.70  
  Purchase #5 $182.68   5.309%   $192.3785   $192.38   $192.40   $192.40  
  Purchase #6 $196.88   8.141%   $212.908   $212.91   $212.90   $212.90  
  Purchase #7 $197.50   11.653%   $220.5147   $220.51   $220.50   $220.50  
  7 purchase totals = $859.50       $931.3024   $931.30   $931.30   $931.20