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	$37.59	13.183%	$42.5455	$42.55	$42.55	$42.50
Purchase #2	$87.78	3.388%	$90.754	$90.75	$90.75	$90.80
Purchase #3	$213.28	12.436%	$239.8035	$239.80	$239.80	$239.80
Purchase #4	$137.38	6.742%	$146.6422	$146.64	$146.65	$146.60
Purchase #5	$210.79	8.715%	$229.1603	$229.16	$229.15	$229.20
Purchase #6	$114.95	8.385%	$124.5886	$124.59	$124.60	$124.60
Purchase #7	$152.34	5.252%	$160.3409	$160.34	$160.35	$160.30
7 purchase totals =	$954.11		$1,033.8350	$1,033.83	$1,033.85	$1,033.80