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	$247.39	12.699%	$278.8061	$278.81	$278.80	$278.80
Purchase #2	$35.29	6.140%	$37.4568	$37.46	$37.45	$37.50
Purchase #3	$236.81	11.159%	$263.2356	$263.24	$263.25	$263.20
Purchase #4	$61.87	13.565%	$70.2627	$70.26	$70.25	$70.30
Purchase #5	$131.28	5.616%	$138.6527	$138.65	$138.65	$138.70
Purchase #6	$234.31	12.803%	$264.3087	$264.31	$264.30	$264.30
Purchase #7	$105.30	7.189%	$112.87	$112.87	$112.85	$112.90
7 purchase totals =	$1,052.25		$1,165.5926	$1,165.60	$1,165.55	$1,165.70