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 $216.53   3.467%   $224.0371   $224.04   $224.05   $224.00  
  Purchase #2 $75.73   9.155%   $82.6631   $82.66   $82.65   $82.70  
  Purchase #3 $107.34   10.491%   $118.601   $118.60   $118.60   $118.60  
  Purchase #4 $97.47   8.560%   $105.8134   $105.81   $105.80   $105.80  
  Purchase #5 $217.45   9.528%   $238.1686   $238.17   $238.15   $238.20  
  Purchase #6 $93.59   8.475%   $101.5218   $101.52   $101.50   $101.50  
  Purchase #7 $9.96   6.613%   $10.6187   $10.62   $10.60   $10.60  
  7 purchase totals = $818.07       $881.4237   $881.42   $881.35   $881.40