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 $61.80   5.796%   $65.3819   $65.38   $65.40   $65.40  
  Purchase #2 $166.87   11.613%   $186.2486   $186.25   $186.25   $186.20  
  Purchase #3 $205.73   13.136%   $232.7547   $232.75   $232.75   $232.80  
  Purchase #4 $139.66   13.321%   $158.2641   $158.26   $158.25   $158.30  
  Purchase #5 $213.54   11.446%   $237.9818   $237.98   $238.00   $238.00  
  Purchase #6 $244.95   10.805%   $271.4168   $271.42   $271.40   $271.40  
  Purchase #7 $15.74   10.809%   $17.4413   $17.44   $17.45   $17.40  
  7 purchase totals = $1,048.29       $1,169.4892   $1,169.48   $1,169.50   $1,169.50