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	$18.31	10.431%	$20.2199	$20.22	$20.20	$20.20
Purchase #2	$97.48	8.234%	$105.5065	$105.51	$105.50	$105.50
Purchase #3	$160.84	5.241%	$169.2696	$169.27	$169.25	$169.30
Purchase #4	$164.93	12.636%	$185.7706	$185.77	$185.75	$185.80
Purchase #5	$244.56	3.755%	$253.7432	$253.74	$253.75	$253.70
Purchase #6	$157.62	9.837%	$173.1251	$173.13	$173.15	$173.10
Purchase #7	$190.48	13.497%	$216.1891	$216.19	$216.20	$216.20
7 purchase totals =	$1,034.22		$1,123.8240	$1,123.83	$1,123.80	$1,123.80