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	$27.26	11.810%	$30.4794	$30.48	$30.50	$30.50
Purchase #2	$62.51	7.449%	$67.1664	$67.17	$67.15	$67.20
Purchase #3	$119.46	6.622%	$127.3706	$127.37	$127.35	$127.40
Purchase #4	$249.29	3.780%	$258.7132	$258.71	$258.70	$258.70
Purchase #5	$66.46	4.631%	$69.5378	$69.54	$69.55	$69.50
Purchase #6	$163.28	4.350%	$170.3827	$170.38	$170.40	$170.40
Purchase #7	$152.43	13.455%	$172.9395	$172.94	$172.95	$172.90
7 purchase totals =	$840.69		$896.5896	$896.59	$896.60	$896.60