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	$37.69	3.552%	$39.0287	$39.03	$39.05	$39.00
Purchase #2	$54.47	11.843%	$60.9209	$60.92	$60.90	$60.90
Purchase #3	$78.50	13.226%	$88.8824	$88.88	$88.90	$88.90
Purchase #4	$53.53	7.612%	$57.6047	$57.60	$57.60	$57.60
Purchase #5	$30.29	9.867%	$33.2787	$33.28	$33.30	$33.30
Purchase #6	$97.27	12.764%	$109.6855	$109.69	$109.70	$109.70
Purchase #7	$113.77	12.321%	$127.7876	$127.79	$127.80	$127.80
7 purchase totals =	$465.52		$517.1885	$517.19	$517.25	$517.20