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	$101.72	4.215%	$106.0075	$106.01	$106.00	$106.00
Purchase #2	$132.98	6.550%	$141.6902	$141.69	$141.70	$141.70
Purchase #3	$243.33	4.538%	$254.3723	$254.37	$254.35	$254.40
Purchase #4	$29.38	9.560%	$32.1887	$32.19	$32.20	$32.20
Purchase #5	$105.81	5.617%	$111.7533	$111.75	$111.75	$111.80
Purchase #6	$16.47	10.763%	$18.2427	$18.24	$18.25	$18.20
Purchase #7	$149.73	10.512%	$165.4696	$165.47	$165.45	$165.50
7 purchase totals =	$779.42		$829.7243	$829.72	$829.70	$829.80