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	$177.39	6.863%	$189.5643	$189.56	$189.55	$189.60
Purchase #2	$237.37	5.507%	$250.442	$250.44	$250.45	$250.40
Purchase #3	$77.49	7.437%	$83.2529	$83.25	$83.25	$83.30
Purchase #4	$135.93	6.371%	$144.5901	$144.59	$144.60	$144.60
Purchase #5	$106.57	4.395%	$111.2538	$111.25	$111.25	$111.30
Purchase #6	$91.65	10.868%	$101.6105	$101.61	$101.60	$101.60
Purchase #7	$123.67	8.388%	$134.0434	$134.04	$134.05	$134.00
7 purchase totals =	$950.07		$1,014.7570	$1,014.74	$1,014.75	$1,014.80