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	$105.56	5.569%	$111.4386	$111.44	$111.45	$111.40
Purchase #2	$63.88	10.566%	$70.6296	$70.63	$70.65	$70.60
Purchase #3	$125.51	12.643%	$141.3782	$141.38	$141.40	$141.40
Purchase #4	$150.35	4.358%	$156.9023	$156.90	$156.90	$156.90
Purchase #5	$52.43	11.366%	$58.3892	$58.39	$58.40	$58.40
Purchase #6	$169.89	11.738%	$189.8317	$189.83	$189.85	$189.80
Purchase #7	$90.38	11.239%	$100.5378	$100.54	$100.55	$100.50
7 purchase totals =	$758.00		$829.1074	$829.11	$829.20	$829.00