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	$25.51	7.422%	$27.4034	$27.40	$27.40	$27.40
Purchase #2	$16.75	11.859%	$18.7364	$18.74	$18.75	$18.70
Purchase #3	$204.89	8.295%	$221.8856	$221.89	$221.90	$221.90
Purchase #4	$99.92	3.574%	$103.4911	$103.49	$103.50	$103.50
Purchase #5	$41.63	9.180%	$45.4516	$45.45	$45.45	$45.50
Purchase #6	$50.45	3.649%	$52.2909	$52.29	$52.30	$52.30
Purchase #7	$146.76	6.833%	$156.7881	$156.79	$156.80	$156.80
7 purchase totals =	$585.91		$626.0471	$626.05	$626.10	$626.10