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	$71.25	10.698%	$78.8723	$78.87	$78.85	$78.90
Purchase #2	$82.42	7.258%	$88.402	$88.40	$88.40	$88.40
Purchase #3	$12.98	4.548%	$13.5703	$13.57	$13.55	$13.60
Purchase #4	$159.98	3.599%	$165.7377	$165.74	$165.75	$165.70
Purchase #5	$125.50	7.846%	$135.3467	$135.35	$135.35	$135.30
Purchase #6	$131.45	9.181%	$143.5184	$143.52	$143.50	$143.50
Purchase #7	$63.31	3.582%	$65.5778	$65.58	$65.60	$65.60
7 purchase totals =	$646.89		$691.0252	$691.03	$691.00	$691.00