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	$39.41	6.372%	$41.9212	$41.92	$41.90	$41.90
Purchase #2	$37.26	13.586%	$42.3221	$42.32	$42.30	$42.30
Purchase #3	$17.41	11.419%	$19.398	$19.40	$19.40	$19.40
Purchase #4	$57.98	7.720%	$62.4561	$62.46	$62.45	$62.50
Purchase #5	$28.38	4.342%	$29.6123	$29.61	$29.60	$29.60
Purchase #6	$100.70	3.833%	$104.5598	$104.56	$104.55	$104.60
Purchase #7	$87.79	3.102%	$90.5132	$90.51	$90.50	$90.50
7 purchase totals =	$368.93		$390.7827	$390.78	$390.70	$390.80