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	$12.70	4.252%	$13.24	$13.24	$13.25	$13.20
Purchase #2	$69.30	3.523%	$71.7414	$71.74	$71.75	$71.70
Purchase #3	$13.29	12.361%	$14.9328	$14.93	$14.95	$14.90
Purchase #4	$56.46	8.540%	$61.2817	$61.28	$61.30	$61.30
Purchase #5	$222.57	9.398%	$243.4871	$243.49	$243.50	$243.50
Purchase #6	$103.58	10.488%	$114.4435	$114.44	$114.45	$114.40
Purchase #7	$34.72	9.176%	$37.9059	$37.91	$37.90	$37.90
7 purchase totals =	$512.62		$557.0324	$557.03	$557.10	$556.90