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	$90.32	10.791%	$100.0664	$100.07	$100.05	$100.10
Purchase #2	$170.68	7.760%	$183.9248	$183.92	$183.90	$183.90
Purchase #3	$158.55	8.592%	$172.1726	$172.17	$172.15	$172.20
Purchase #4	$110.99	5.179%	$116.7382	$116.74	$116.75	$116.70
Purchase #5	$213.53	12.534%	$240.2939	$240.29	$240.30	$240.30
Purchase #6	$85.32	3.297%	$88.133	$88.13	$88.15	$88.10
Purchase #7	$52.47	4.267%	$54.7089	$54.71	$54.70	$54.70
7 purchase totals =	$881.86		$956.0378	$956.03	$956.00	$956.00