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	$180.34	4.496%	$188.4481	$188.45	$188.45	$188.40
Purchase #2	$57.59	13.186%	$65.1838	$65.18	$65.20	$65.20
Purchase #3	$152.52	3.454%	$157.788	$157.79	$157.80	$157.80
Purchase #4	$243.56	4.733%	$255.0877	$255.09	$255.10	$255.10
Purchase #5	$178.43	6.865%	$190.6792	$190.68	$190.70	$190.70
Purchase #6	$130.89	8.104%	$141.4973	$141.50	$141.50	$141.50
Purchase #7	$123.42	4.605%	$129.1035	$129.10	$129.10	$129.10
7 purchase totals =	$1,066.75		$1,127.7876	$1,127.79	$1,127.85	$1,127.80