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 $65.77   12.669%   $74.1024   $74.10   $74.10   $74.10  
  Purchase #2 $33.63   7.593%   $36.1835   $36.18   $36.20   $36.20  
  Purchase #3 $233.36   4.674%   $244.2672   $244.27   $244.25   $244.30  
  Purchase #4 $152.79   5.494%   $161.1843   $161.18   $161.20   $161.20  
  Purchase #5 $161.68   13.181%   $182.991   $182.99   $183.00   $183.00  
  Purchase #6 $156.62   9.539%   $171.56   $171.56   $171.55   $171.60  
  Purchase #7 $68.26   12.229%   $76.6075   $76.61   $76.60   $76.60  
  7 purchase totals = $872.11       $946.8959   $946.89   $946.90   $947.00