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	$100.55	11.224%	$111.8357	$111.84	$111.85	$111.80
Purchase #2	$127.96	9.351%	$139.9255	$139.93	$139.95	$139.90
Purchase #3	$50.44	5.569%	$53.249	$53.25	$53.25	$53.20
Purchase #4	$39.88	7.828%	$43.0018	$43.00	$43.00	$43.00
Purchase #5	$215.72	6.393%	$229.511	$229.51	$229.50	$229.50
Purchase #6	$160.61	7.551%	$172.7377	$172.74	$172.75	$172.70
Purchase #7	$22.25	9.209%	$24.299	$24.30	$24.30	$24.30
7 purchase totals =	$717.41		$774.5597	$774.57	$774.60	$774.40