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	$91.95	6.678%	$98.0904	$98.09	$98.10	$98.10
Purchase #2	$60.68	8.148%	$65.6242	$65.62	$65.60	$65.60
Purchase #3	$16.50	9.807%	$18.1182	$18.12	$18.10	$18.10
Purchase #4	$104.64	11.401%	$116.57	$116.57	$116.55	$116.60
Purchase #5	$56.56	8.297%	$61.2528	$61.25	$61.25	$61.30
Purchase #6	$191.55	13.753%	$217.8939	$217.89	$217.90	$217.90
Purchase #7	$96.75	6.225%	$102.7727	$102.77	$102.75	$102.80
7 purchase totals =	$618.63		$680.3222	$680.31	$680.25	$680.40