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 $183.77   5.564%   $193.995   $194.00   $194.00   $194.00  
  Purchase #2 $139.94   8.149%   $151.3437   $151.34   $151.35   $151.30  
  Purchase #3 $162.65   12.822%   $183.505   $183.51   $183.50   $183.50  
  Purchase #4 $87.81   11.308%   $97.7396   $97.74   $97.75   $97.70  
  Purchase #5 $15.86   5.115%   $16.6712   $16.67   $16.65   $16.70  
  Purchase #6 $152.59   4.554%   $159.5389   $159.54   $159.55   $159.50  
  Purchase #7 $96.38   4.846%   $101.0506   $101.05   $101.05   $101.10  
  7 purchase totals = $839.00       $903.8440   $903.85   $903.85   $903.80