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	$152.80	4.528%	$159.7188	$159.72	$159.70	$159.70
Purchase #2	$247.98	13.217%	$280.7555	$280.76	$280.75	$280.80
Purchase #3	$202.92	11.176%	$225.5983	$225.60	$225.60	$225.60
Purchase #4	$152.85	5.258%	$160.8869	$160.89	$160.90	$160.90
Purchase #5	$195.36	13.602%	$221.9329	$221.93	$221.95	$221.90
Purchase #6	$96.53	3.433%	$99.8439	$99.84	$99.85	$99.80
Purchase #7	$206.89	11.451%	$230.581	$230.58	$230.60	$230.60
7 purchase totals =	$1,255.33		$1,379.3173	$1,379.32	$1,379.35	$1,379.30