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	$48.74	5.202%	$51.2755	$51.28	$51.30	$51.30
Purchase #2	$90.92	11.115%	$101.0258	$101.03	$101.05	$101.00
Purchase #3	$197.59	5.854%	$209.1569	$209.16	$209.15	$209.20
Purchase #4	$95.61	13.217%	$108.2468	$108.25	$108.25	$108.20
Purchase #5	$83.71	9.208%	$91.418	$91.42	$91.40	$91.40
Purchase #6	$75.87	3.432%	$78.4739	$78.47	$78.45	$78.50
Purchase #7	$172.38	10.317%	$190.1644	$190.16	$190.15	$190.20
7 purchase totals =	$764.82		$829.7613	$829.77	$829.75	$829.80