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	$88.93	10.750%	$98.49	$98.49	$98.50	$98.50
Purchase #2	$99.81	8.368%	$108.1621	$108.16	$108.15	$108.20
Purchase #3	$85.60	4.244%	$89.2329	$89.23	$89.25	$89.20
Purchase #4	$110.30	8.196%	$119.3402	$119.34	$119.35	$119.30
Purchase #5	$20.54	4.415%	$21.4468	$21.45	$21.45	$21.40
Purchase #6	$151.60	13.274%	$171.7234	$171.72	$171.70	$171.70
Purchase #7	$183.92	8.225%	$199.0474	$199.05	$199.05	$199.00
7 purchase totals =	$740.70		$807.4428	$807.44	$807.45	$807.30