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 $113.84   8.160%   $123.1293   $123.13   $123.15   $123.10  
  Purchase #2 $15.49   7.255%   $16.6138   $16.61   $16.60   $16.60  
  Purchase #3 $43.84   3.845%   $45.5256   $45.53   $45.55   $45.50  
  Purchase #4 $101.91   9.163%   $111.248   $111.25   $111.25   $111.20  
  Purchase #5 $97.76   11.246%   $108.7541   $108.75   $108.75   $108.80  
  Purchase #6 $89.25   6.401%   $94.9629   $94.96   $94.95   $95.00  
  Purchase #7 $164.82   5.550%   $173.9675   $173.97   $173.95   $174.00  
  7 purchase totals = $626.91       $674.2012   $674.20   $674.20   $674.20