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	$129.94	10.833%	$144.0164	$144.02	$144.00	$144.00
Purchase #2	$76.75	4.720%	$80.3726	$80.37	$80.35	$80.40
Purchase #3	$244.84	11.443%	$272.857	$272.86	$272.85	$272.90
Purchase #4	$36.28	4.496%	$37.9111	$37.91	$37.90	$37.90
Purchase #5	$41.91	4.191%	$43.6664	$43.67	$43.65	$43.70
Purchase #6	$38.28	3.742%	$39.7124	$39.71	$39.70	$39.70
Purchase #7	$64.44	5.139%	$67.7516	$67.75	$67.75	$67.80
7 purchase totals =	$632.44		$686.2875	$686.29	$686.20	$686.40