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	$72.87	10.862%	$80.7851	$80.79	$80.80	$80.80
Purchase #2	$133.51	5.785%	$141.2336	$141.23	$141.25	$141.20
Purchase #3	$11.36	10.815%	$12.5886	$12.59	$12.60	$12.60
Purchase #4	$231.70	13.284%	$262.479	$262.48	$262.50	$262.50
Purchase #5	$231.45	3.722%	$240.0646	$240.06	$240.05	$240.10
Purchase #6	$36.42	6.292%	$38.7115	$38.71	$38.70	$38.70
Purchase #7	$95.53	10.556%	$105.6141	$105.61	$105.60	$105.60
7 purchase totals =	$812.84		$881.4765	$881.47	$881.50	$881.50