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	$155.53	6.405%	$165.4917	$165.49	$165.50	$165.50
Purchase #2	$178.47	3.809%	$185.2679	$185.27	$185.25	$185.30
Purchase #3	$17.86	10.762%	$19.7821	$19.78	$19.80	$19.80
Purchase #4	$88.75	10.228%	$97.8274	$97.83	$97.85	$97.80
Purchase #5	$225.92	7.246%	$242.2902	$242.29	$242.30	$242.30
Purchase #6	$33.34	13.485%	$37.8359	$37.84	$37.85	$37.80
Purchase #7	$104.94	7.371%	$112.6751	$112.68	$112.70	$112.70
7 purchase totals =	$804.81		$861.1703	$861.18	$861.25	$861.20