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 $59.49   7.262%   $63.8102   $63.81   $63.80   $63.80  
  Purchase #2 $217.96   3.120%   $224.7604   $224.76   $224.75   $224.80  
  Purchase #3 $48.81   4.729%   $51.1182   $51.12   $51.10   $51.10  
  Purchase #4 $73.43   4.609%   $76.8144   $76.81   $76.80   $76.80  
  Purchase #5 $67.70   4.846%   $70.9807   $70.98   $71.00   $71.00  
  Purchase #6 $57.86   9.464%   $63.3359   $63.34   $63.35   $63.30  
  Purchase #7 $204.47   4.381%   $213.4278   $213.43   $213.45   $213.40  
  7 purchase totals = $729.72       $764.2476   $764.25   $764.25   $764.20