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	$209.49	12.139%	$234.92	$234.92	$234.90	$234.90
Purchase #2	$239.39	6.724%	$255.4866	$255.49	$255.50	$255.50
Purchase #3	$244.73	13.608%	$278.0329	$278.03	$278.05	$278.00
Purchase #4	$79.98	4.498%	$83.5775	$83.58	$83.60	$83.60
Purchase #5	$10.52	8.805%	$11.4463	$11.45	$11.45	$11.40
Purchase #6	$159.88	3.700%	$165.7956	$165.80	$165.80	$165.80
Purchase #7	$162.29	11.818%	$181.4694	$181.47	$181.45	$181.50
7 purchase totals =	$1,106.28		$1,210.7283	$1,210.74	$1,210.75	$1,210.70