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	$81.61	9.669%	$89.5009	$89.50	$89.50	$89.50
Purchase #2	$141.87	3.506%	$146.844	$146.84	$146.85	$146.80
Purchase #3	$46.74	12.517%	$52.5904	$52.59	$52.60	$52.60
Purchase #4	$224.38	8.745%	$244.002	$244.00	$244.00	$244.00
Purchase #5	$20.32	6.282%	$21.5965	$21.60	$21.60	$21.60
Purchase #6	$213.79	11.605%	$238.6003	$238.60	$238.60	$238.60
Purchase #7	$26.81	12.525%	$30.168	$30.17	$30.15	$30.20
7 purchase totals =	$755.52		$823.3021	$823.30	$823.30	$823.30