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	$43.92	12.477%	$49.3999	$49.40	$49.40	$49.40
Purchase #2	$238.29	5.254%	$250.8098	$250.81	$250.80	$250.80
Purchase #3	$184.30	5.391%	$194.2356	$194.24	$194.25	$194.20
Purchase #4	$118.78	11.392%	$132.3114	$132.31	$132.30	$132.30
Purchase #5	$65.37	10.865%	$72.4725	$72.47	$72.45	$72.50
Purchase #6	$109.28	8.242%	$118.2869	$118.29	$118.30	$118.30
Purchase #7	$42.48	10.751%	$47.047	$47.05	$47.05	$47.00
7 purchase totals =	$802.42		$864.5631	$864.57	$864.55	$864.50