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	$53.44	12.148%	$59.9319	$59.93	$59.95	$59.90
Purchase #2	$157.62	11.598%	$175.9008	$175.90	$175.90	$175.90
Purchase #3	$137.61	12.310%	$154.5498	$154.55	$154.55	$154.50
Purchase #4	$58.28	3.345%	$60.2295	$60.23	$60.25	$60.20
Purchase #5	$31.55	11.621%	$35.2164	$35.22	$35.20	$35.20
Purchase #6	$38.53	3.331%	$39.8134	$39.81	$39.80	$39.80
Purchase #7	$53.51	7.608%	$57.581	$57.58	$57.60	$57.60
7 purchase totals =	$530.54		$583.2228	$583.22	$583.25	$583.10