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	$25.81	11.265%	$28.7175	$28.72	$28.70	$28.70
Purchase #2	$72.89	6.364%	$77.5287	$77.53	$77.55	$77.50
Purchase #3	$102.30	7.683%	$110.1597	$110.16	$110.15	$110.20
Purchase #4	$72.68	9.406%	$79.5163	$79.52	$79.50	$79.50
Purchase #5	$64.66	12.620%	$72.8201	$72.82	$72.80	$72.80
Purchase #6	$182.54	5.681%	$192.9101	$192.91	$192.90	$192.90
Purchase #7	$163.40	13.733%	$185.8397	$185.84	$185.85	$185.80
7 purchase totals =	$684.28		$747.4921	$747.50	$747.45	$747.40