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	$106.99	4.210%	$111.4943	$111.49	$111.50	$111.50
Purchase #2	$223.39	12.657%	$251.6645	$251.66	$251.65	$251.70
Purchase #3	$165.51	6.414%	$176.1258	$176.13	$176.15	$176.10
Purchase #4	$128.86	5.704%	$136.2102	$136.21	$136.20	$136.20
Purchase #5	$67.68	8.809%	$73.6419	$73.64	$73.65	$73.60
Purchase #6	$60.57	11.381%	$67.4635	$67.46	$67.45	$67.50
Purchase #7	$124.89	13.210%	$141.388	$141.39	$141.40	$141.40
7 purchase totals =	$877.89		$957.9882	$957.98	$958.00	$958.00