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	$231.27	11.748%	$258.4396	$258.44	$258.45	$258.40
Purchase #2	$214.96	6.412%	$228.7432	$228.74	$228.75	$228.70
Purchase #3	$145.94	13.141%	$165.118	$165.12	$165.10	$165.10
Purchase #4	$72.72	7.607%	$78.2518	$78.25	$78.25	$78.30
Purchase #5	$115.36	9.300%	$126.0885	$126.09	$126.10	$126.10
Purchase #6	$130.80	6.382%	$139.1477	$139.15	$139.15	$139.10
Purchase #7	$72.91	3.802%	$75.682	$75.68	$75.70	$75.70
7 purchase totals =	$983.96		$1,071.4708	$1,071.47	$1,071.50	$1,071.40