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 $215.99   12.164%   $242.263   $242.26   $242.25   $242.30  
  Purchase #2 $87.63   9.186%   $95.6797   $95.68   $95.70   $95.70  
  Purchase #3 $244.73   12.414%   $275.1108   $275.11   $275.10   $275.10  
  Purchase #4 $169.98   12.817%   $191.7663   $191.77   $191.75   $191.80  
  Purchase #5 $83.25   12.796%   $93.9027   $93.90   $93.90   $93.90  
  Purchase #6 $26.83   5.381%   $28.2737   $28.27   $28.25   $28.30  
  Purchase #7 $49.94   13.722%   $56.7928   $56.79   $56.80   $56.80  
  7 purchase totals = $878.35       $983.7890   $983.78   $983.75   $983.90