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	$158.32	13.728%	$180.0542	$180.05	$180.05	$180.10
Purchase #2	$112.72	13.811%	$128.2878	$128.29	$128.30	$128.30
Purchase #3	$53.51	8.714%	$58.1729	$58.17	$58.15	$58.20
Purchase #4	$71.68	13.142%	$81.1002	$81.10	$81.10	$81.10
Purchase #5	$161.54	4.417%	$168.6752	$168.68	$168.70	$168.70
Purchase #6	$118.47	7.388%	$127.2226	$127.22	$127.20	$127.20
Purchase #7	$85.86	8.188%	$92.8902	$92.89	$92.90	$92.90
7 purchase totals =	$762.10		$836.4031	$836.40	$836.40	$836.50