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	$50.65	5.393%	$53.3816	$53.38	$53.40	$53.40
Purchase #2	$157.69	10.271%	$173.8863	$173.89	$173.90	$173.90
Purchase #3	$158.71	8.360%	$171.9782	$171.98	$172.00	$172.00
Purchase #4	$25.43	11.519%	$28.3593	$28.36	$28.35	$28.40
Purchase #5	$53.80	5.137%	$56.5637	$56.56	$56.55	$56.60
Purchase #6	$46.31	9.236%	$50.5872	$50.59	$50.60	$50.60
Purchase #7	$105.92	13.431%	$120.1461	$120.15	$120.15	$120.10
7 purchase totals =	$598.51		$654.9024	$654.91	$654.95	$655.00