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	$146.67	8.433%	$159.0387	$159.04	$159.05	$159.00
Purchase #2	$38.27	4.477%	$39.9833	$39.98	$40.00	$40.00
Purchase #3	$151.86	13.807%	$172.8273	$172.83	$172.85	$172.80
Purchase #4	$190.55	8.109%	$206.0017	$206.00	$206.00	$206.00
Purchase #5	$249.85	10.599%	$276.3316	$276.33	$276.35	$276.30
Purchase #6	$23.79	3.250%	$24.5632	$24.56	$24.55	$24.60
Purchase #7	$138.81	9.368%	$151.8137	$151.81	$151.80	$151.80
7 purchase totals =	$939.80		$1,030.5595	$1,030.55	$1,030.60	$1,030.50