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 $195.26   4.636%   $204.3123   $204.31   $204.30   $204.30  
  Purchase #2 $94.52   3.556%   $97.8811   $97.88   $97.90   $97.90  
  Purchase #3 $12.49   7.142%   $13.382   $13.38   $13.40   $13.40  
  Purchase #4 $224.39   6.392%   $238.733   $238.73   $238.75   $238.70  
  Purchase #5 $112.68   10.339%   $124.33   $124.33   $124.35   $124.30  
  Purchase #6 $43.64   11.525%   $48.6695   $48.67   $48.65   $48.70  
  Purchase #7 $248.80   12.128%   $278.9745   $278.97   $278.95   $279.00  
  7 purchase totals = $931.78       $1,006.2824   $1,006.27   $1,006.30   $1,006.30