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	$136.32	10.829%	$151.0821	$151.08	$151.10	$151.10
Purchase #2	$23.64	4.859%	$24.7887	$24.79	$24.80	$24.80
Purchase #3	$12.91	3.286%	$13.3342	$13.33	$13.35	$13.30
Purchase #4	$80.32	12.860%	$90.6492	$90.65	$90.65	$90.60
Purchase #5	$102.73	6.561%	$109.4701	$109.47	$109.45	$109.50
Purchase #6	$226.78	5.339%	$238.8878	$238.89	$238.90	$238.90
Purchase #7	$246.59	10.559%	$272.6274	$272.63	$272.65	$272.60
7 purchase totals =	$829.29		$900.8395	$900.84	$900.90	$900.80