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	$58.34	9.389%	$63.8175	$63.82	$63.80	$63.80
Purchase #2	$242.89	13.443%	$275.5417	$275.54	$275.55	$275.50
Purchase #3	$77.82	3.857%	$80.8215	$80.82	$80.80	$80.80
Purchase #4	$48.42	10.488%	$53.4983	$53.50	$53.50	$53.50
Purchase #5	$88.77	12.801%	$100.1334	$100.13	$100.15	$100.10
Purchase #6	$90.75	11.437%	$101.1291	$101.13	$101.15	$101.10
Purchase #7	$242.68	4.218%	$252.9162	$252.92	$252.90	$252.90
7 purchase totals =	$849.67		$927.8577	$927.86	$927.85	$927.70