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	$165.94	12.447%	$186.5946	$186.59	$186.60	$186.60
Purchase #2	$42.98	11.517%	$47.93	$47.93	$47.95	$47.90
Purchase #3	$12.40	8.309%	$13.4303	$13.43	$13.45	$13.40
Purchase #4	$158.27	9.606%	$173.4734	$173.47	$173.45	$173.50
Purchase #5	$100.29	4.465%	$104.7679	$104.77	$104.75	$104.80
Purchase #6	$122.64	3.807%	$127.3089	$127.31	$127.30	$127.30
Purchase #7	$159.51	8.760%	$173.4831	$173.48	$173.50	$173.50
7 purchase totals =	$762.03		$826.9882	$826.98	$827.00	$827.00