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	$17.97	3.434%	$18.5871	$18.59	$18.60	$18.60
Purchase #2	$47.46	8.752%	$51.6137	$51.61	$51.60	$51.60
Purchase #3	$146.78	10.596%	$162.3328	$162.33	$162.35	$162.30
Purchase #4	$217.59	3.531%	$225.2731	$225.27	$225.25	$225.30
Purchase #5	$130.87	9.571%	$143.3956	$143.40	$143.40	$143.40
Purchase #6	$129.86	6.363%	$138.123	$138.12	$138.10	$138.10
Purchase #7	$247.76	12.333%	$278.3162	$278.32	$278.30	$278.30
7 purchase totals =	$938.29		$1,017.6415	$1,017.64	$1,017.60	$1,017.60