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	$104.25	13.499%	$118.3227	$118.32	$118.30	$118.30
Purchase #2	$117.82	6.487%	$125.463	$125.46	$125.45	$125.50
Purchase #3	$11.78	13.284%	$13.3449	$13.34	$13.35	$13.30
Purchase #4	$106.76	4.574%	$111.6432	$111.64	$111.65	$111.60
Purchase #5	$99.71	12.532%	$112.2057	$112.21	$112.20	$112.20
Purchase #6	$15.56	13.426%	$17.6491	$17.65	$17.65	$17.60
Purchase #7	$25.28	13.592%	$28.7161	$28.72	$28.70	$28.70
7 purchase totals =	$481.16		$527.3447	$527.34	$527.30	$527.20