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	$42.42	7.733%	$45.7003	$45.70	$45.70	$45.70
Purchase #2	$63.76	10.211%	$70.2705	$70.27	$70.25	$70.30
Purchase #3	$153.97	7.748%	$165.8996	$165.90	$165.90	$165.90
Purchase #4	$171.72	4.273%	$179.0576	$179.06	$179.05	$179.10
Purchase #5	$218.90	4.689%	$229.1642	$229.16	$229.15	$229.20
Purchase #6	$34.88	9.710%	$38.2668	$38.27	$38.25	$38.30
Purchase #7	$165.59	3.694%	$171.7069	$171.71	$171.70	$171.70
7 purchase totals =	$851.24		$900.0659	$900.07	$900.00	$900.20