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 $238.41   11.577%   $266.0107   $266.01   $266.00   $266.00  
  Purchase #2 $171.88   8.597%   $186.6565   $186.66   $186.65   $186.70  
  Purchase #3 $49.38   3.422%   $51.0698   $51.07   $51.05   $51.10  
  Purchase #4 $159.38   12.636%   $179.5193   $179.52   $179.50   $179.50  
  Purchase #5 $82.94   5.442%   $87.4536   $87.45   $87.45   $87.50  
  Purchase #6 $249.28   7.213%   $267.2606   $267.26   $267.25   $267.30  
  Purchase #7 $193.81   12.279%   $217.6079   $217.61   $217.60   $217.60  
  7 purchase totals = $1,145.08       $1,255.5784   $1,255.58   $1,255.50   $1,255.70