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	$155.78	6.519%	$165.9353	$165.94	$165.95	$165.90
Purchase #2	$118.36	7.535%	$127.2784	$127.28	$127.30	$127.30
Purchase #3	$122.43	4.181%	$127.5488	$127.55	$127.55	$127.50
Purchase #4	$32.82	7.819%	$35.3862	$35.39	$35.40	$35.40
Purchase #5	$237.56	13.508%	$269.6496	$269.65	$269.65	$269.60
Purchase #6	$33.95	5.386%	$35.7785	$35.78	$35.80	$35.80
Purchase #7	$160.60	10.102%	$176.8238	$176.82	$176.80	$176.80
7 purchase totals =	$861.50		$938.4006	$938.41	$938.45	$938.30