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	$112.32	7.620%	$120.8788	$120.88	$120.90	$120.90
Purchase #2	$177.34	13.271%	$200.8748	$200.87	$200.85	$200.90
Purchase #3	$159.81	12.585%	$179.9221	$179.92	$179.90	$179.90
Purchase #4	$10.89	11.540%	$12.1467	$12.15	$12.15	$12.10
Purchase #5	$31.89	7.331%	$34.2279	$34.23	$34.25	$34.20
Purchase #6	$60.28	9.698%	$66.126	$66.13	$66.15	$66.10
Purchase #7	$248.30	4.145%	$258.592	$258.59	$258.60	$258.60
7 purchase totals =	$800.83		$872.7683	$872.77	$872.80	$872.70