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 $53.53   9.733%   $58.7401   $58.74   $58.75   $58.70  
  Purchase #2 $218.93   7.448%   $235.2359   $235.24   $235.25   $235.20  
  Purchase #3 $139.51   8.454%   $151.3042   $151.30   $151.30   $151.30  
  Purchase #4 $49.36   5.128%   $51.8912   $51.89   $51.90   $51.90  
  Purchase #5 $182.28   6.225%   $193.6269   $193.63   $193.65   $193.60  
  Purchase #6 $147.25   6.565%   $156.917   $156.92   $156.90   $156.90  
  Purchase #7 $77.42   6.215%   $82.2317   $82.23   $82.25   $82.20  
  7 purchase totals = $868.28       $929.9470   $929.95   $930.00   $929.80