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	$45.66	10.660%	$50.5274	$50.53	$50.55	$50.50
Purchase #2	$101.66	7.663%	$109.4502	$109.45	$109.45	$109.50
Purchase #3	$132.49	9.656%	$145.2832	$145.28	$145.30	$145.30
Purchase #4	$71.70	9.570%	$78.5617	$78.56	$78.55	$78.60
Purchase #5	$78.95	13.652%	$89.7283	$89.73	$89.75	$89.70
Purchase #6	$173.92	9.354%	$190.1885	$190.19	$190.20	$190.20
Purchase #7	$194.56	4.251%	$202.8307	$202.83	$202.85	$202.80
7 purchase totals =	$798.94		$866.5700	$866.57	$866.65	$866.60