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	$223.77	3.316%	$231.1902	$231.19	$231.20	$231.20
Purchase #2	$71.46	3.351%	$73.8546	$73.85	$73.85	$73.90
Purchase #3	$123.83	13.813%	$140.9346	$140.93	$140.95	$140.90
Purchase #4	$18.50	9.354%	$20.2305	$20.23	$20.25	$20.20
Purchase #5	$157.81	9.164%	$172.2717	$172.27	$172.25	$172.30
Purchase #6	$13.78	12.636%	$15.5212	$15.52	$15.50	$15.50
Purchase #7	$172.80	9.261%	$188.803	$188.80	$188.80	$188.80
7 purchase totals =	$781.95		$842.8058	$842.79	$842.80	$842.80