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	$150.91	9.674%	$165.509	$165.51	$165.50	$165.50
Purchase #2	$123.73	5.840%	$130.9558	$130.96	$130.95	$131.00
Purchase #3	$219.76	10.810%	$243.5161	$243.52	$243.50	$243.50
Purchase #4	$150.42	3.442%	$155.5975	$155.60	$155.60	$155.60
Purchase #5	$172.84	12.420%	$194.3067	$194.31	$194.30	$194.30
Purchase #6	$34.74	13.779%	$39.5268	$39.53	$39.55	$39.50
Purchase #7	$37.45	8.472%	$40.6228	$40.62	$40.60	$40.60
7 purchase totals =	$889.85		$970.0347	$970.05	$970.00	$970.00