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	$40.39	13.348%	$45.7813	$45.78	$45.80	$45.80
Purchase #2	$79.34	3.120%	$81.8154	$81.82	$81.80	$81.80
Purchase #3	$70.88	10.589%	$78.3855	$78.39	$78.40	$78.40
Purchase #4	$26.65	7.745%	$28.714	$28.71	$28.70	$28.70
Purchase #5	$203.70	7.314%	$218.5986	$218.60	$218.60	$218.60
Purchase #6	$189.92	10.540%	$209.9376	$209.94	$209.95	$209.90
Purchase #7	$133.97	5.491%	$141.3263	$141.33	$141.35	$141.30
7 purchase totals =	$744.85		$804.5587	$804.57	$804.60	$804.50