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 $168.95   9.619%   $185.2013   $185.20   $185.20   $185.20  
  Purchase #2 $128.83   12.232%   $144.5885   $144.59   $144.60   $144.60  
  Purchase #3 $177.92   5.742%   $188.1362   $188.14   $188.15   $188.10  
  Purchase #4 $224.64   10.162%   $247.4679   $247.47   $247.45   $247.50  
  Purchase #5 $49.63   3.381%   $51.308   $51.31   $51.30   $51.30  
  Purchase #6 $174.54   4.793%   $182.9057   $182.91   $182.90   $182.90  
  Purchase #7 $135.81   13.488%   $154.1281   $154.13   $154.15   $154.10  
  7 purchase totals = $1,060.32       $1,153.7357   $1,153.75   $1,153.75   $1,153.70