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	$99.87	10.250%	$110.1067	$110.11	$110.10	$110.10
Purchase #2	$130.87	13.712%	$148.8149	$148.81	$148.80	$148.80
Purchase #3	$231.93	10.548%	$256.394	$256.39	$256.40	$256.40
Purchase #4	$195.37	10.672%	$216.2199	$216.22	$216.20	$216.20
Purchase #5	$48.63	5.800%	$51.4505	$51.45	$51.45	$51.50
Purchase #6	$71.54	10.371%	$78.9594	$78.96	$78.95	$79.00
Purchase #7	$151.94	3.667%	$157.5116	$157.51	$157.50	$157.50
7 purchase totals =	$930.15		$1,019.4570	$1,019.45	$1,019.40	$1,019.50