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 $86.27   6.465%   $91.8474   $91.85   $91.85   $91.80  
  Purchase #2 $23.63   11.297%   $26.2995   $26.30   $26.30   $26.30  
  Purchase #3 $5.99   12.552%   $6.7419   $6.74   $6.75   $6.70  
  Purchase #4 $124.48   12.251%   $139.73   $139.73   $139.75   $139.70  
  Purchase #5 $45.95   5.863%   $48.644   $48.64   $48.65   $48.60  
  Purchase #6 $73.72   11.175%   $81.9582   $81.96   $81.95   $82.00  
  Purchase #7 $76.68   3.818%   $79.6076   $79.61   $79.60   $79.60  
  7 purchase totals = $436.72       $474.8286   $474.83   $474.85   $474.70