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	$146.41	13.138%	$165.6453	$165.65	$165.65	$165.60
Purchase #2	$170.44	10.251%	$187.9118	$187.91	$187.90	$187.90
Purchase #3	$123.39	11.589%	$137.6897	$137.69	$137.70	$137.70
Purchase #4	$141.72	3.839%	$147.1606	$147.16	$147.15	$147.20
Purchase #5	$225.25	12.680%	$253.8117	$253.81	$253.80	$253.80
Purchase #6	$194.46	5.103%	$204.3833	$204.38	$204.40	$204.40
Purchase #7	$29.75	5.536%	$31.397	$31.40	$31.40	$31.40
7 purchase totals =	$1,031.42		$1,127.9994	$1,128.00	$1,128.00	$1,128.00