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	$244.53	11.382%	$272.3624	$272.36	$272.35	$272.40
Purchase #2	$76.89	7.345%	$82.5376	$82.54	$82.55	$82.50
Purchase #3	$77.83	5.478%	$82.0935	$82.09	$82.10	$82.10
Purchase #4	$183.47	5.514%	$193.5865	$193.59	$193.60	$193.60
Purchase #5	$166.46	11.731%	$185.9874	$185.99	$186.00	$186.00
Purchase #6	$137.64	5.146%	$144.723	$144.72	$144.70	$144.70
Purchase #7	$33.25	4.546%	$34.7615	$34.76	$34.75	$34.80
7 purchase totals =	$920.07		$996.0519	$996.05	$996.05	$996.10