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 $244.37   10.197%   $269.2884   $269.29   $269.30   $269.30  
  Purchase #2 $118.93   13.584%   $135.0855   $135.09   $135.10   $135.10  
  Purchase #3 $128.86   8.484%   $139.7925   $139.79   $139.80   $139.80  
  Purchase #4 $72.29   13.619%   $82.1352   $82.14   $82.15   $82.10  
  Purchase #5 $66.67   11.808%   $74.5424   $74.54   $74.55   $74.50  
  Purchase #6 $245.26   11.712%   $273.9849   $273.98   $274.00   $274.00  
  Purchase #7 $184.63   3.195%   $190.5289   $190.53   $190.55   $190.50  
  7 purchase totals = $1,061.01       $1,165.3578   $1,165.36   $1,165.45   $1,165.30