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 $31.29   3.676%   $32.4402   $32.44   $32.45   $32.40  
  Purchase #2 $149.59   11.137%   $166.2498   $166.25   $166.25   $166.20  
  Purchase #3 $14.33   11.622%   $15.9954   $16.00   $16.00   $16.00  
  Purchase #4 $159.61   4.349%   $166.5514   $166.55   $166.55   $166.60  
  Purchase #5 $85.50   7.545%   $91.951   $91.95   $91.95   $92.00  
  Purchase #6 $141.34   3.105%   $145.7286   $145.73   $145.75   $145.70  
  Purchase #7 $177.36   3.314%   $183.2377   $183.24   $183.25   $183.20  
  7 purchase totals = $759.02       $802.1541   $802.16   $802.20   $802.10