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	$114.34	4.534%	$119.5242	$119.52	$119.50	$119.50
Purchase #2	$137.45	6.680%	$146.6317	$146.63	$146.65	$146.60
Purchase #3	$75.89	7.302%	$81.4315	$81.43	$81.45	$81.40
Purchase #4	$35.43	7.735%	$38.1705	$38.17	$38.15	$38.20
Purchase #5	$91.40	4.448%	$95.4655	$95.47	$95.45	$95.50
Purchase #6	$38.40	4.123%	$39.9832	$39.98	$40.00	$40.00
Purchase #7	$242.35	13.764%	$275.7071	$275.71	$275.70	$275.70
7 purchase totals =	$735.26		$796.9137	$796.91	$796.90	$796.90