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	$153.78	9.288%	$168.0631	$168.06	$168.05	$168.10
Purchase #2	$213.60	11.542%	$238.2537	$238.25	$238.25	$238.30
Purchase #3	$134.83	7.483%	$144.9193	$144.92	$144.90	$144.90
Purchase #4	$247.92	8.111%	$268.0288	$268.03	$268.05	$268.00
Purchase #5	$105.84	8.551%	$114.8904	$114.89	$114.90	$114.90
Purchase #6	$59.83	10.754%	$66.2641	$66.26	$66.25	$66.30
Purchase #7	$111.56	6.422%	$118.7244	$118.72	$118.70	$118.70
7 purchase totals =	$1,027.36		$1,119.1438	$1,119.13	$1,119.10	$1,119.20