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	$105.92	5.374%	$111.6121	$111.61	$111.60	$111.60
Purchase #2	$49.58	12.840%	$55.9461	$55.95	$55.95	$55.90
Purchase #3	$235.80	8.315%	$255.4068	$255.41	$255.40	$255.40
Purchase #4	$120.95	8.792%	$131.5839	$131.58	$131.60	$131.60
Purchase #5	$155.35	12.762%	$175.1758	$175.18	$175.20	$175.20
Purchase #6	$201.36	6.392%	$214.2309	$214.23	$214.25	$214.20
Purchase #7	$244.48	11.247%	$271.9767	$271.98	$272.00	$272.00
7 purchase totals =	$1,113.44		$1,215.9323	$1,215.94	$1,216.00	$1,215.90