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	$143.64	11.712%	$160.4631	$160.46	$160.45	$160.50
Purchase #2	$35.70	8.764%	$38.8287	$38.83	$38.85	$38.80
Purchase #3	$186.89	10.604%	$206.7078	$206.71	$206.70	$206.70
Purchase #4	$11.38	10.784%	$12.6072	$12.61	$12.60	$12.60
Purchase #5	$117.42	8.247%	$127.1036	$127.10	$127.10	$127.10
Purchase #6	$19.87	12.701%	$22.3937	$22.39	$22.40	$22.40
Purchase #7	$244.74	8.650%	$265.91	$265.91	$265.90	$265.90
7 purchase totals =	$759.64		$834.0141	$834.01	$834.00	$834.00