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	$133.88	4.466%	$139.8591	$139.86	$139.85	$139.90
Purchase #2	$81.92	10.837%	$90.7977	$90.80	$90.80	$90.80
Purchase #3	$245.32	5.217%	$258.1183	$258.12	$258.10	$258.10
Purchase #4	$58.57	10.255%	$64.5764	$64.58	$64.60	$64.60
Purchase #5	$244.34	12.849%	$275.7352	$275.74	$275.75	$275.70
Purchase #6	$155.89	10.639%	$172.4751	$172.48	$172.50	$172.50
Purchase #7	$18.80	6.343%	$19.9925	$19.99	$20.00	$20.00
7 purchase totals =	$938.72		$1,021.5543	$1,021.57	$1,021.60	$1,021.60