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	$66.42	6.431%	$70.6915	$70.69	$70.70	$70.70
Purchase #2	$91.98	12.583%	$103.5538	$103.55	$103.55	$103.60
Purchase #3	$90.62	10.396%	$100.0409	$100.04	$100.05	$100.00
Purchase #4	$31.57	7.158%	$33.8298	$33.83	$33.85	$33.80
Purchase #5	$209.32	6.692%	$223.3277	$223.33	$223.35	$223.30
Purchase #6	$95.28	7.199%	$102.1392	$102.14	$102.15	$102.10
Purchase #7	$129.43	11.853%	$144.7713	$144.77	$144.75	$144.80
7 purchase totals =	$714.62		$778.3542	$778.35	$778.40	$778.30