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	$16.29	12.204%	$18.278	$18.28	$18.30	$18.30
Purchase #2	$62.65	8.164%	$67.7647	$67.76	$67.75	$67.80
Purchase #3	$218.76	13.643%	$248.6054	$248.61	$248.60	$248.60
Purchase #4	$147.77	13.393%	$167.5608	$167.56	$167.55	$167.60
Purchase #5	$159.86	6.281%	$169.9008	$169.90	$169.90	$169.90
Purchase #6	$49.33	11.466%	$54.9862	$54.99	$55.00	$55.00
Purchase #7	$66.56	5.659%	$70.3266	$70.33	$70.35	$70.30
7 purchase totals =	$721.22		$797.4225	$797.43	$797.45	$797.50