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	$74.57	10.675%	$82.5303	$82.53	$82.55	$82.50
Purchase #2	$249.90	10.290%	$275.6147	$275.61	$275.60	$275.60
Purchase #3	$77.49	8.698%	$84.2301	$84.23	$84.25	$84.20
Purchase #4	$181.40	5.659%	$191.6654	$191.67	$191.65	$191.70
Purchase #5	$97.26	3.823%	$100.9782	$100.98	$101.00	$101.00
Purchase #6	$89.33	12.429%	$100.4328	$100.43	$100.45	$100.40
Purchase #7	$5.54	4.108%	$5.7676	$5.77	$5.75	$5.80
7 purchase totals =	$775.49		$841.2191	$841.22	$841.25	$841.20