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 $183.47   6.404%   $195.2194   $195.22   $195.20   $195.20  
  Purchase #2 $123.71   5.588%   $130.6229   $130.62   $130.60   $130.60  
  Purchase #3 $14.47   5.770%   $15.3049   $15.30   $15.30   $15.30  
  Purchase #4 $70.57   6.193%   $74.9404   $74.94   $74.95   $74.90  
  Purchase #5 $190.71   10.657%   $211.034   $211.03   $211.05   $211.00  
  Purchase #6 $118.91   6.316%   $126.4204   $126.42   $126.40   $126.40  
  Purchase #7 $205.94   9.860%   $226.2457   $226.25   $226.25   $226.20  
  7 purchase totals = $907.78       $979.7877   $979.78   $979.75   $979.60