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 $50.39   6.138%   $53.4829   $53.48   $53.50   $53.50  
  Purchase #2 $222.84   10.169%   $245.5006   $245.50   $245.50   $245.50  
  Purchase #3 $217.53   7.681%   $234.2385   $234.24   $234.25   $234.20  
  Purchase #4 $171.98   11.770%   $192.222   $192.22   $192.20   $192.20  
  Purchase #5 $74.63   10.442%   $82.4229   $82.42   $82.40   $82.40  
  Purchase #6 $14.27   7.117%   $15.2856   $15.29   $15.30   $15.30  
  Purchase #7 $182.33   7.480%   $195.9683   $195.97   $195.95   $196.00  
  7 purchase totals = $933.97       $1,019.1208   $1,019.12   $1,019.10   $1,019.10