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	$154.61	11.863%	$172.9514	$172.95	$172.95	$173.00
Purchase #2	$69.43	12.572%	$78.1587	$78.16	$78.15	$78.20
Purchase #3	$194.79	10.776%	$215.7806	$215.78	$215.80	$215.80
Purchase #4	$127.49	13.568%	$144.7878	$144.79	$144.80	$144.80
Purchase #5	$63.37	10.803%	$70.2159	$70.22	$70.20	$70.20
Purchase #6	$39.56	6.567%	$42.1579	$42.16	$42.15	$42.20
Purchase #7	$229.61	12.835%	$259.0804	$259.08	$259.10	$259.10
7 purchase totals =	$878.86		$983.1327	$983.14	$983.15	$983.30