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	$63.46	4.757%	$66.4788	$66.48	$66.50	$66.50
Purchase #2	$35.26	11.807%	$39.4231	$39.42	$39.40	$39.40
Purchase #3	$11.31	9.144%	$12.3442	$12.34	$12.35	$12.30
Purchase #4	$18.69	10.826%	$20.7134	$20.71	$20.70	$20.70
Purchase #5	$190.28	11.442%	$212.0518	$212.05	$212.05	$212.10
Purchase #6	$244.94	12.468%	$275.4791	$275.48	$275.50	$275.50
Purchase #7	$136.47	11.242%	$151.812	$151.81	$151.80	$151.80
7 purchase totals =	$700.41		$778.3024	$778.29	$778.30	$778.30