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	$146.90	6.507%	$156.4588	$156.46	$156.45	$156.50
Purchase #2	$167.38	8.779%	$182.0743	$182.07	$182.05	$182.10
Purchase #3	$128.59	12.662%	$144.8721	$144.87	$144.85	$144.90
Purchase #4	$161.33	5.725%	$170.5661	$170.57	$170.55	$170.60
Purchase #5	$84.52	9.349%	$92.4218	$92.42	$92.40	$92.40
Purchase #6	$105.53	7.151%	$113.0765	$113.08	$113.10	$113.10
Purchase #7	$90.60	10.453%	$100.0704	$100.07	$100.05	$100.10
7 purchase totals =	$884.85		$959.5400	$959.54	$959.45	$959.70