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	$70.25	4.582%	$73.4689	$73.47	$73.45	$73.50
Purchase #2	$246.47	6.677%	$262.9268	$262.93	$262.95	$262.90
Purchase #3	$44.36	9.437%	$48.5463	$48.55	$48.55	$48.50
Purchase #4	$57.69	8.254%	$62.4517	$62.45	$62.45	$62.50
Purchase #5	$60.67	4.523%	$63.4141	$63.41	$63.40	$63.40
Purchase #6	$53.26	4.388%	$55.597	$55.60	$55.60	$55.60
Purchase #7	$88.75	11.775%	$99.2003	$99.20	$99.20	$99.20
7 purchase totals =	$621.45		$665.6051	$665.61	$665.60	$665.60