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	$35.27	7.182%	$37.8031	$37.80	$37.80	$37.80
Purchase #2	$139.32	13.341%	$157.9067	$157.91	$157.90	$157.90
Purchase #3	$70.43	13.392%	$79.862	$79.86	$79.85	$79.90
Purchase #4	$56.57	9.728%	$62.0731	$62.07	$62.05	$62.10
Purchase #5	$109.72	8.727%	$119.2953	$119.30	$119.30	$119.30
Purchase #6	$52.75	5.745%	$55.7805	$55.78	$55.80	$55.80
Purchase #7	$159.33	5.254%	$167.7012	$167.70	$167.70	$167.70
7 purchase totals =	$623.39		$680.4219	$680.42	$680.40	$680.50