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	$45.78	12.750%	$51.617	$51.62	$51.60	$51.60
Purchase #2	$80.31	11.760%	$89.7545	$89.75	$89.75	$89.80
Purchase #3	$96.52	4.621%	$100.9802	$100.98	$101.00	$101.00
Purchase #4	$124.68	10.548%	$137.8312	$137.83	$137.85	$137.80
Purchase #5	$165.51	13.612%	$188.0392	$188.04	$188.05	$188.00
Purchase #6	$198.69	13.536%	$225.5847	$225.58	$225.60	$225.60
Purchase #7	$223.34	9.480%	$244.5126	$244.51	$244.50	$244.50
7 purchase totals =	$934.83		$1,038.3194	$1,038.31	$1,038.35	$1,038.30