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	$120.90	6.525%	$128.7887	$128.79	$128.80	$128.80
Purchase #2	$33.35	6.315%	$35.4561	$35.46	$35.45	$35.50
Purchase #3	$105.25	10.871%	$116.6917	$116.69	$116.70	$116.70
Purchase #4	$9.42	12.423%	$10.5902	$10.59	$10.60	$10.60
Purchase #5	$34.46	9.613%	$37.7726	$37.77	$37.75	$37.80
Purchase #6	$125.42	9.518%	$137.3575	$137.36	$137.35	$137.40
Purchase #7	$136.63	13.709%	$155.3606	$155.36	$155.35	$155.40
7 purchase totals =	$565.43		$622.0174	$622.02	$622.00	$622.20