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	$79.59	5.464%	$83.9388	$83.94	$83.95	$83.90
Purchase #2	$14.76	12.388%	$16.5885	$16.59	$16.60	$16.60
Purchase #3	$139.52	8.562%	$151.4657	$151.47	$151.45	$151.50
Purchase #4	$109.69	6.624%	$116.9559	$116.96	$116.95	$117.00
Purchase #5	$63.81	5.260%	$67.1664	$67.17	$67.15	$67.20
Purchase #6	$159.40	7.635%	$171.5702	$171.57	$171.55	$171.60
Purchase #7	$68.57	12.528%	$77.1604	$77.16	$77.15	$77.20
7 purchase totals =	$635.34		$684.8459	$684.86	$684.80	$685.00