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 $92.52   5.484%   $97.5938   $97.59   $97.60   $97.60  
  Purchase #2 $119.35   13.798%   $135.8179   $135.82   $135.80   $135.80  
  Purchase #3 $163.43   13.141%   $184.9063   $184.91   $184.90   $184.90  
  Purchase #4 $54.99   10.580%   $60.8079   $60.81   $60.80   $60.80  
  Purchase #5 $105.44   9.331%   $115.2786   $115.28   $115.30   $115.30  
  Purchase #6 $39.55   5.593%   $41.762   $41.76   $41.75   $41.80  
  Purchase #7 $140.25   7.209%   $150.3606   $150.36   $150.35   $150.40  
  7 purchase totals = $715.53       $786.5271   $786.53   $786.50   $786.60