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	$144.28	3.794%	$149.754	$149.75	$149.75	$149.80
Purchase #2	$136.48	10.456%	$150.7503	$150.75	$150.75	$150.80
Purchase #3	$184.82	10.536%	$204.2926	$204.29	$204.30	$204.30
Purchase #4	$99.40	12.285%	$111.6113	$111.61	$111.60	$111.60
Purchase #5	$150.97	7.471%	$162.249	$162.25	$162.25	$162.20
Purchase #6	$9.25	13.296%	$10.4799	$10.48	$10.50	$10.50
Purchase #7	$73.74	13.314%	$83.5577	$83.56	$83.55	$83.60
7 purchase totals =	$798.94		$872.6948	$872.69	$872.70	$872.80