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	$103.55	12.701%	$116.7019	$116.70	$116.70	$116.70
Purchase #2	$90.67	11.295%	$100.9112	$100.91	$100.90	$100.90
Purchase #3	$212.47	5.174%	$223.4632	$223.46	$223.45	$223.50
Purchase #4	$235.54	13.207%	$266.6478	$266.65	$266.65	$266.60
Purchase #5	$38.50	7.332%	$41.3228	$41.32	$41.30	$41.30
Purchase #6	$125.35	10.275%	$138.2297	$138.23	$138.25	$138.20
Purchase #7	$29.86	13.243%	$33.8144	$33.81	$33.80	$33.80
7 purchase totals =	$835.94		$921.0910	$921.08	$921.05	$921.00