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 $33.95   6.157%   $36.0403   $36.04   $36.05   $36.00  
  Purchase #2 $240.98   10.580%   $266.4757   $266.48   $266.50   $266.50  
  Purchase #3 $15.50   5.143%   $16.2972   $16.30   $16.30   $16.30  
  Purchase #4 $167.38   5.677%   $176.8822   $176.88   $176.90   $176.90  
  Purchase #5 $14.92   13.742%   $16.9703   $16.97   $16.95   $17.00  
  Purchase #6 $134.80   12.194%   $151.2375   $151.24   $151.25   $151.20  
  Purchase #7 $9.71   11.536%   $10.8301   $10.83   $10.85   $10.80  
  7 purchase totals = $617.24       $674.7333   $674.74   $674.80   $674.70