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	$138.87	5.711%	$146.8009	$146.80	$146.80	$146.80
Purchase #2	$249.68	7.682%	$268.8604	$268.86	$268.85	$268.90
Purchase #3	$137.38	10.777%	$152.1854	$152.19	$152.20	$152.20
Purchase #4	$17.85	6.248%	$18.9653	$18.97	$18.95	$19.00
Purchase #5	$94.34	6.687%	$100.6485	$100.65	$100.65	$100.60
Purchase #6	$96.39	6.275%	$102.4385	$102.44	$102.45	$102.40
Purchase #7	$247.72	3.298%	$255.8898	$255.89	$255.90	$255.90
7 purchase totals =	$982.23		$1,045.7888	$1,045.80	$1,045.80	$1,045.80