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	$126.99	5.649%	$134.1637	$134.16	$134.15	$134.20
Purchase #2	$55.60	6.801%	$59.3814	$59.38	$59.40	$59.40
Purchase #3	$167.94	13.569%	$190.7278	$190.73	$190.75	$190.70
Purchase #4	$135.42	5.182%	$142.4375	$142.44	$142.45	$142.40
Purchase #5	$118.63	13.281%	$134.3853	$134.39	$134.40	$134.40
Purchase #6	$59.41	5.544%	$62.7037	$62.70	$62.70	$62.70
Purchase #7	$118.46	11.825%	$132.4679	$132.47	$132.45	$132.50
7 purchase totals =	$782.45		$856.2673	$856.27	$856.30	$856.30