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	$21.35	3.572%	$22.1126	$22.11	$22.10	$22.10
Purchase #2	$119.71	10.281%	$132.0174	$132.02	$132.00	$132.00
Purchase #3	$106.73	4.206%	$111.2191	$111.22	$111.20	$111.20
Purchase #4	$57.34	6.651%	$61.1537	$61.15	$61.15	$61.20
Purchase #5	$29.44	10.293%	$32.4703	$32.47	$32.45	$32.50
Purchase #6	$121.32	9.514%	$132.8624	$132.86	$132.85	$132.90
Purchase #7	$63.30	11.162%	$70.3655	$70.37	$70.35	$70.40
7 purchase totals =	$519.19		$562.2010	$562.20	$562.10	$562.30