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	$165.87	11.754%	$185.3664	$185.37	$185.35	$185.40
Purchase #2	$188.86	11.593%	$210.7545	$210.75	$210.75	$210.80
Purchase #3	$242.90	13.297%	$275.1984	$275.20	$275.20	$275.20
Purchase #4	$232.29	4.320%	$242.3249	$242.32	$242.30	$242.30
Purchase #5	$234.47	10.714%	$259.5911	$259.59	$259.60	$259.60
Purchase #6	$172.60	3.676%	$178.9448	$178.94	$178.95	$178.90
Purchase #7	$128.72	8.812%	$140.0628	$140.06	$140.05	$140.10
7 purchase totals =	$1,365.71		$1,492.2429	$1,492.23	$1,492.20	$1,492.30