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	$30.46	11.526%	$33.9708	$33.97	$33.95	$34.00
Purchase #2	$137.75	10.264%	$151.8887	$151.89	$151.90	$151.90
Purchase #3	$141.64	8.199%	$153.2531	$153.25	$153.25	$153.30
Purchase #4	$144.96	9.159%	$158.2369	$158.24	$158.25	$158.20
Purchase #5	$92.40	8.548%	$100.2984	$100.30	$100.30	$100.30
Purchase #6	$16.26	4.774%	$17.0363	$17.04	$17.05	$17.00
Purchase #7	$161.72	11.585%	$180.4553	$180.46	$180.45	$180.50
7 purchase totals =	$725.19		$795.1395	$795.15	$795.15	$795.20