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 $59.74   13.121%   $67.5785   $67.58   $67.60   $67.60  
  Purchase #2 $68.59   4.531%   $71.6978   $71.70   $71.70   $71.70  
  Purchase #3 $53.96   4.172%   $56.2112   $56.21   $56.20   $56.20  
  Purchase #4 $102.60   12.363%   $115.2844   $115.28   $115.30   $115.30  
  Purchase #5 $72.52   4.409%   $75.7174   $75.72   $75.70   $75.70  
  Purchase #6 $232.74   5.113%   $244.64   $244.64   $244.65   $244.60  
  Purchase #7 $89.77   8.312%   $97.2317   $97.23   $97.25   $97.20  
  7 purchase totals = $679.92       $728.3610   $728.36   $728.40   $728.30