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	$18.79	13.178%	$21.2661	$21.27	$21.25	$21.30
Purchase #2	$15.26	4.415%	$15.9337	$15.93	$15.95	$15.90
Purchase #3	$140.53	7.784%	$151.4689	$151.47	$151.45	$151.50
Purchase #4	$204.94	12.735%	$231.0391	$231.04	$231.05	$231.00
Purchase #5	$250.56	12.407%	$281.647	$281.65	$281.65	$281.60
Purchase #6	$100.57	4.787%	$105.3843	$105.38	$105.40	$105.40
Purchase #7	$17.80	6.380%	$18.9356	$18.94	$18.95	$18.90
7 purchase totals =	$748.45		$825.6747	$825.68	$825.70	$825.60