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	$238.81	7.165%	$255.9207	$255.92	$255.90	$255.90
Purchase #2	$144.27	9.350%	$157.7592	$157.76	$157.75	$157.80
Purchase #3	$18.83	12.612%	$21.2048	$21.20	$21.20	$21.20
Purchase #4	$233.67	9.526%	$255.9294	$255.93	$255.95	$255.90
Purchase #5	$141.34	6.160%	$150.0465	$150.05	$150.05	$150.00
Purchase #6	$42.79	13.633%	$48.6236	$48.62	$48.60	$48.60
Purchase #7	$28.78	8.124%	$31.1181	$31.12	$31.10	$31.10
7 purchase totals =	$848.49		$920.6023	$920.60	$920.55	$920.50