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	$131.82	6.437%	$140.3053	$140.31	$140.30	$140.30
Purchase #2	$100.34	3.738%	$104.0907	$104.09	$104.10	$104.10
Purchase #3	$225.64	11.820%	$252.3106	$252.31	$252.30	$252.30
Purchase #4	$118.51	13.336%	$134.3145	$134.31	$134.30	$134.30
Purchase #5	$159.46	3.686%	$165.3377	$165.34	$165.35	$165.30
Purchase #6	$151.63	13.795%	$172.5474	$172.55	$172.55	$172.50
Purchase #7	$190.87	7.151%	$204.5191	$204.52	$204.50	$204.50
7 purchase totals =	$1,078.27		$1,173.4253	$1,173.43	$1,173.40	$1,173.30