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	$125.37	11.222%	$139.439	$139.44	$139.45	$139.40
Purchase #2	$187.55	12.107%	$210.2567	$210.26	$210.25	$210.30
Purchase #3	$67.65	4.846%	$70.9283	$70.93	$70.95	$70.90
Purchase #4	$123.77	10.113%	$136.2869	$136.29	$136.30	$136.30
Purchase #5	$102.60	8.169%	$110.9814	$110.98	$111.00	$111.00
Purchase #6	$228.52	9.194%	$249.5301	$249.53	$249.55	$249.50
Purchase #7	$211.48	10.370%	$233.4105	$233.41	$233.40	$233.40
7 purchase totals =	$1,046.94		$1,150.8329	$1,150.84	$1,150.90	$1,150.80