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	$54.73	6.262%	$58.1572	$58.16	$58.15	$58.20
Purchase #2	$159.56	6.751%	$170.3319	$170.33	$170.35	$170.30
Purchase #3	$152.72	8.134%	$165.1422	$165.14	$165.15	$165.10
Purchase #4	$153.72	7.277%	$164.9062	$164.91	$164.90	$164.90
Purchase #5	$110.67	11.569%	$123.4734	$123.47	$123.45	$123.50
Purchase #6	$140.29	4.275%	$146.2874	$146.29	$146.30	$146.30
Purchase #7	$219.62	5.124%	$230.8733	$230.87	$230.85	$230.90
7 purchase totals =	$991.31		$1,059.1716	$1,059.17	$1,059.15	$1,059.20