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	$55.95	6.198%	$59.4178	$59.42	$59.40	$59.40
Purchase #2	$52.69	3.799%	$54.6917	$54.69	$54.70	$54.70
Purchase #3	$83.92	7.252%	$90.0059	$90.01	$90.00	$90.00
Purchase #4	$117.91	10.320%	$130.0783	$130.08	$130.10	$130.10
Purchase #5	$107.99	10.668%	$119.5104	$119.51	$119.50	$119.50
Purchase #6	$131.45	11.300%	$146.3039	$146.30	$146.30	$146.30
Purchase #7	$57.34	5.278%	$60.3664	$60.37	$60.35	$60.40
7 purchase totals =	$607.25		$660.3744	$660.38	$660.35	$660.40