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	$86.48	4.353%	$90.2445	$90.24	$90.25	$90.20
Purchase #2	$237.25	7.181%	$254.2869	$254.29	$254.30	$254.30
Purchase #3	$116.79	8.490%	$126.7055	$126.71	$126.70	$126.70
Purchase #4	$225.58	5.809%	$238.6839	$238.68	$238.70	$238.70
Purchase #5	$30.33	13.771%	$34.5067	$34.51	$34.50	$34.50
Purchase #6	$101.32	10.421%	$111.8786	$111.88	$111.90	$111.90
Purchase #7	$26.86	7.421%	$28.8533	$28.85	$28.85	$28.90
7 purchase totals =	$824.61		$885.1594	$885.16	$885.20	$885.20