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	$158.30	8.689%	$172.0547	$172.05	$172.05	$172.10
Purchase #2	$247.32	10.459%	$273.1872	$273.19	$273.20	$273.20
Purchase #3	$139.40	4.864%	$146.1804	$146.18	$146.20	$146.20
Purchase #4	$96.31	4.563%	$100.7046	$100.70	$100.70	$100.70
Purchase #5	$22.33	4.343%	$23.2998	$23.30	$23.30	$23.30
Purchase #6	$68.46	13.183%	$77.4851	$77.49	$77.50	$77.50
Purchase #7	$99.33	13.229%	$112.4704	$112.47	$112.45	$112.50
7 purchase totals =	$831.45		$905.3822	$905.38	$905.40	$905.50