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	$221.89	3.467%	$229.5829	$229.58	$229.60	$229.60
Purchase #2	$193.93	7.621%	$208.7094	$208.71	$208.70	$208.70
Purchase #3	$21.83	3.125%	$22.5122	$22.51	$22.50	$22.50
Purchase #4	$179.67	9.381%	$196.5248	$196.52	$196.50	$196.50
Purchase #5	$73.68	12.240%	$82.6984	$82.70	$82.70	$82.70
Purchase #6	$154.92	4.466%	$161.8387	$161.84	$161.85	$161.80
Purchase #7	$184.78	7.407%	$198.4667	$198.47	$198.45	$198.50
7 purchase totals =	$1,030.70		$1,100.3331	$1,100.33	$1,100.30	$1,100.30