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	$197.59	9.770%	$216.8945	$216.89	$216.90	$216.90
Purchase #2	$151.88	11.739%	$169.7092	$169.71	$169.70	$169.70
Purchase #3	$183.62	6.800%	$196.1062	$196.11	$196.10	$196.10
Purchase #4	$86.98	3.569%	$90.0843	$90.08	$90.10	$90.10
Purchase #5	$131.45	5.253%	$138.3551	$138.36	$138.35	$138.40
Purchase #6	$36.29	6.407%	$38.6151	$38.62	$38.60	$38.60
Purchase #7	$58.30	13.370%	$66.0947	$66.09	$66.10	$66.10
7 purchase totals =	$846.11		$915.8591	$915.86	$915.85	$915.90