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	$94.99	4.740%	$99.4925	$99.49	$99.50	$99.50
Purchase #2	$137.80	10.261%	$151.9397	$151.94	$151.95	$151.90
Purchase #3	$207.84	13.382%	$235.6531	$235.65	$235.65	$235.70
Purchase #4	$238.89	9.696%	$262.0528	$262.05	$262.05	$262.10
Purchase #5	$233.33	9.291%	$255.0087	$255.01	$255.00	$255.00
Purchase #6	$14.58	6.476%	$15.5242	$15.52	$15.50	$15.50
Purchase #7	$153.31	11.436%	$170.8425	$170.84	$170.85	$170.80
7 purchase totals =	$1,080.74		$1,190.5135	$1,190.50	$1,190.50	$1,190.50