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	$85.73	3.345%	$88.5977	$88.60	$88.60	$88.60
Purchase #2	$100.32	10.667%	$111.0211	$111.02	$111.00	$111.00
Purchase #3	$176.84	4.752%	$185.2434	$185.24	$185.25	$185.20
Purchase #4	$235.68	6.255%	$250.4218	$250.42	$250.40	$250.40
Purchase #5	$96.90	9.112%	$105.7295	$105.73	$105.75	$105.70
Purchase #6	$175.55	9.175%	$191.6567	$191.66	$191.65	$191.70
Purchase #7	$69.61	6.161%	$73.8987	$73.90	$73.90	$73.90
7 purchase totals =	$940.63		$1,006.5689	$1,006.57	$1,006.55	$1,006.50