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	$127.61	13.476%	$144.8067	$144.81	$144.80	$144.80
Purchase #2	$105.68	13.345%	$119.783	$119.78	$119.80	$119.80
Purchase #3	$15.90	10.762%	$17.6112	$17.61	$17.60	$17.60
Purchase #4	$53.75	10.275%	$59.2728	$59.27	$59.25	$59.30
Purchase #5	$202.51	11.321%	$225.4362	$225.44	$225.45	$225.40
Purchase #6	$93.92	3.409%	$97.1217	$97.12	$97.10	$97.10
Purchase #7	$229.31	3.574%	$237.5055	$237.51	$237.50	$237.50
7 purchase totals =	$828.68		$901.5371	$901.54	$901.50	$901.50