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	$24.30	12.118%	$27.2447	$27.24	$27.25	$27.20
Purchase #2	$74.61	11.108%	$82.8977	$82.90	$82.90	$82.90
Purchase #3	$244.86	4.457%	$255.7734	$255.77	$255.75	$255.80
Purchase #4	$34.78	8.582%	$37.7648	$37.76	$37.75	$37.80
Purchase #5	$19.92	12.868%	$22.4833	$22.48	$22.50	$22.50
Purchase #6	$122.31	3.360%	$126.4196	$126.42	$126.40	$126.40
Purchase #7	$69.45	3.787%	$72.0801	$72.08	$72.10	$72.10
7 purchase totals =	$590.23		$624.6636	$624.65	$624.65	$624.70