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	$57.40	12.768%	$64.7288	$64.73	$64.75	$64.70
Purchase #2	$165.74	4.288%	$172.8469	$172.85	$172.85	$172.80
Purchase #3	$248.71	11.578%	$277.5056	$277.51	$277.50	$277.50
Purchase #4	$114.98	4.176%	$119.7816	$119.78	$119.80	$119.80
Purchase #5	$92.29	12.546%	$103.8687	$103.87	$103.85	$103.90
Purchase #6	$159.83	10.372%	$176.4076	$176.41	$176.40	$176.40
Purchase #7	$114.96	8.275%	$124.4729	$124.47	$124.45	$124.50
7 purchase totals =	$953.91		$1,039.6121	$1,039.62	$1,039.60	$1,039.60