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 $47.39   10.744%   $52.4816   $52.48   $52.50   $52.50  
  Purchase #2 $138.98   13.429%   $157.6436   $157.64   $157.65   $157.60  
  Purchase #3 $71.43   7.507%   $76.7923   $76.79   $76.80   $76.80  
  Purchase #4 $191.86   11.223%   $213.3924   $213.39   $213.40   $213.40  
  Purchase #5 $57.78   5.458%   $60.9336   $60.93   $60.95   $60.90  
  Purchase #6 $229.76   11.549%   $256.295   $256.30   $256.30   $256.30  
  Purchase #7 $224.80   6.852%   $240.2033   $240.20   $240.20   $240.20  
  7 purchase totals = $962.00       $1,057.7418   $1,057.73   $1,057.80   $1,057.70