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	$102.99	8.156%	$111.3899	$111.39	$111.40	$111.40
Purchase #2	$118.81	9.704%	$130.3393	$130.34	$130.35	$130.30
Purchase #3	$151.27	4.260%	$157.7141	$157.71	$157.70	$157.70
Purchase #4	$200.89	8.383%	$217.7306	$217.73	$217.75	$217.70
Purchase #5	$223.57	13.380%	$253.4837	$253.48	$253.50	$253.50
Purchase #6	$129.92	12.688%	$146.4042	$146.40	$146.40	$146.40
Purchase #7	$239.49	4.592%	$250.4874	$250.49	$250.50	$250.50
7 purchase totals =	$1,166.94		$1,267.5492	$1,267.54	$1,267.60	$1,267.50