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	$109.57	9.583%	$120.0701	$120.07	$120.05	$120.10
Purchase #2	$11.94	13.127%	$13.5074	$13.51	$13.50	$13.50
Purchase #3	$147.71	12.732%	$166.5164	$166.52	$166.50	$166.50
Purchase #4	$245.45	12.346%	$275.7533	$275.75	$275.75	$275.80
Purchase #5	$41.61	12.341%	$46.7451	$46.75	$46.75	$46.70
Purchase #6	$36.37	4.274%	$37.9245	$37.92	$37.90	$37.90
Purchase #7	$235.91	8.483%	$255.9222	$255.92	$255.90	$255.90
7 purchase totals =	$828.56		$916.4390	$916.44	$916.35	$916.40