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	$19.54	3.706%	$20.2642	$20.26	$20.25	$20.30
Purchase #2	$197.75	12.296%	$222.0653	$222.07	$222.05	$222.10
Purchase #3	$138.59	12.328%	$155.6754	$155.68	$155.70	$155.70
Purchase #4	$37.64	7.519%	$40.4702	$40.47	$40.45	$40.50
Purchase #5	$33.39	8.864%	$36.3497	$36.35	$36.35	$36.30
Purchase #6	$98.94	12.298%	$111.1076	$111.11	$111.10	$111.10
Purchase #7	$74.46	7.575%	$80.1003	$80.10	$80.10	$80.10
7 purchase totals =	$600.31		$666.0327	$666.04	$666.00	$666.10