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	$40.56	11.662%	$45.2901	$45.29	$45.30	$45.30
Purchase #2	$57.66	3.371%	$59.6037	$59.60	$59.60	$59.60
Purchase #3	$62.47	13.867%	$71.1327	$71.13	$71.15	$71.10
Purchase #4	$84.49	7.816%	$91.0937	$91.09	$91.10	$91.10
Purchase #5	$106.33	9.160%	$116.0698	$116.07	$116.05	$116.10
Purchase #6	$48.81	3.795%	$50.6623	$50.66	$50.65	$50.70
Purchase #7	$72.71	3.157%	$75.0055	$75.01	$75.00	$75.00
7 purchase totals =	$473.03		$508.8578	$508.85	$508.85	$508.90