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	$114.39	6.532%	$121.862	$121.86	$121.85	$121.90
Purchase #2	$52.44	9.859%	$57.6101	$57.61	$57.60	$57.60
Purchase #3	$7.91	6.816%	$8.4491	$8.45	$8.45	$8.40
Purchase #4	$141.45	9.788%	$155.2951	$155.30	$155.30	$155.30
Purchase #5	$100.35	4.738%	$105.1046	$105.10	$105.10	$105.10
Purchase #6	$160.67	7.642%	$172.9484	$172.95	$172.95	$172.90
Purchase #7	$64.43	7.483%	$69.2513	$69.25	$69.25	$69.30
7 purchase totals =	$641.64		$690.5206	$690.52	$690.50	$690.50