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	$123.48	10.200%	$136.075	$136.08	$136.10	$136.10
Purchase #2	$143.29	13.290%	$162.3332	$162.33	$162.35	$162.30
Purchase #3	$61.27	9.139%	$66.8695	$66.87	$66.85	$66.90
Purchase #4	$199.80	7.554%	$214.8929	$214.89	$214.90	$214.90
Purchase #5	$81.95	4.458%	$85.6033	$85.60	$85.60	$85.60
Purchase #6	$209.58	9.853%	$230.2299	$230.23	$230.25	$230.20
Purchase #7	$127.27	11.330%	$141.6897	$141.69	$141.70	$141.70
7 purchase totals =	$946.64		$1,037.6935	$1,037.69	$1,037.75	$1,037.70