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	$179.46	7.769%	$193.4022	$193.40	$193.40	$193.40
Purchase #2	$83.63	9.509%	$91.5824	$91.58	$91.60	$91.60
Purchase #3	$81.83	13.398%	$92.7936	$92.79	$92.80	$92.80
Purchase #4	$23.47	3.387%	$24.2649	$24.26	$24.25	$24.30
Purchase #5	$81.34	11.286%	$90.52	$90.52	$90.50	$90.50
Purchase #6	$128.31	8.550%	$139.2805	$139.28	$139.30	$139.30
Purchase #7	$175.98	8.849%	$191.5525	$191.55	$191.55	$191.60
7 purchase totals =	$754.02		$823.3961	$823.38	$823.40	$823.50