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 $119.44   12.403%   $134.2541   $134.25   $134.25   $134.30  
  Purchase #2 $84.87   13.161%   $96.0397   $96.04   $96.05   $96.00  
  Purchase #3 $242.67   5.246%   $255.4005   $255.40   $255.40   $255.40  
  Purchase #4 $163.92   3.570%   $169.7719   $169.77   $169.75   $169.80  
  Purchase #5 $71.35   11.118%   $79.2827   $79.28   $79.30   $79.30  
  Purchase #6 $51.32   11.368%   $57.1541   $57.15   $57.15   $57.20  
  Purchase #7 $161.88   12.184%   $181.6035   $181.60   $181.60   $181.60  
  7 purchase totals = $895.45       $973.5065   $973.49   $973.50   $973.60