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	$140.84	10.522%	$155.6592	$155.66	$155.65	$155.70
Purchase #2	$152.64	8.482%	$165.5869	$165.59	$165.60	$165.60
Purchase #3	$72.50	13.815%	$82.5159	$82.52	$82.50	$82.50
Purchase #4	$31.89	9.527%	$34.9282	$34.93	$34.95	$34.90
Purchase #5	$224.46	9.546%	$245.887	$245.89	$245.90	$245.90
Purchase #6	$33.62	4.695%	$35.1985	$35.20	$35.20	$35.20
Purchase #7	$191.95	8.422%	$208.116	$208.12	$208.10	$208.10
7 purchase totals =	$847.90		$927.8917	$927.91	$927.90	$927.90