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	$122.31	3.619%	$126.7364	$126.74	$126.75	$126.70
Purchase #2	$71.52	9.377%	$78.2264	$78.23	$78.25	$78.20
Purchase #3	$35.47	8.851%	$38.6094	$38.61	$38.60	$38.60
Purchase #4	$88.83	11.647%	$99.176	$99.18	$99.20	$99.20
Purchase #5	$231.95	10.301%	$255.8432	$255.84	$255.85	$255.80
Purchase #6	$123.65	12.214%	$138.7526	$138.75	$138.75	$138.80
Purchase #7	$99.58	9.200%	$108.7414	$108.74	$108.75	$108.70
7 purchase totals =	$773.31		$846.0854	$846.09	$846.15	$846.00