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	$89.57	12.637%	$100.889	$100.89	$100.90	$100.90
Purchase #2	$171.56	8.567%	$186.2575	$186.26	$186.25	$186.30
Purchase #3	$118.54	3.699%	$122.9248	$122.92	$122.90	$122.90
Purchase #4	$32.28	12.672%	$36.3705	$36.37	$36.35	$36.40
Purchase #5	$48.33	13.468%	$54.8391	$54.84	$54.85	$54.80
Purchase #6	$70.56	10.102%	$77.688	$77.69	$77.70	$77.70
Purchase #7	$70.45	8.554%	$76.4763	$76.48	$76.50	$76.50
7 purchase totals =	$601.29		$655.4452	$655.45	$655.45	$655.50