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	$63.35	4.700%	$66.3275	$66.33	$66.35	$66.30
Purchase #2	$221.35	9.400%	$242.1569	$242.16	$242.15	$242.20
Purchase #3	$90.42	11.231%	$100.5751	$100.58	$100.60	$100.60
Purchase #4	$199.33	5.652%	$210.5961	$210.60	$210.60	$210.60
Purchase #5	$35.90	7.744%	$38.6801	$38.68	$38.70	$38.70
Purchase #6	$242.89	4.278%	$253.2808	$253.28	$253.30	$253.30
Purchase #7	$7.28	6.702%	$7.7679	$7.77	$7.75	$7.80
7 purchase totals =	$860.52		$919.3844	$919.40	$919.45	$919.50