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	$36.43	4.633%	$38.1178	$38.12	$38.10	$38.10
Purchase #2	$59.76	12.787%	$67.4015	$67.40	$67.40	$67.40
Purchase #3	$138.34	4.628%	$144.7424	$144.74	$144.75	$144.70
Purchase #4	$15.48	10.678%	$17.133	$17.13	$17.15	$17.10
Purchase #5	$68.90	13.609%	$78.2766	$78.28	$78.30	$78.30
Purchase #6	$103.60	5.137%	$108.9219	$108.92	$108.90	$108.90
Purchase #7	$139.83	11.326%	$155.6671	$155.67	$155.65	$155.70
7 purchase totals =	$562.34		$610.2603	$610.26	$610.25	$610.20