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	$37.43	9.393%	$40.9458	$40.95	$40.95	$40.90
Purchase #2	$173.93	5.439%	$183.3901	$183.39	$183.40	$183.40
Purchase #3	$166.31	11.693%	$185.7566	$185.76	$185.75	$185.80
Purchase #4	$189.29	12.320%	$212.6105	$212.61	$212.60	$212.60
Purchase #5	$172.82	11.761%	$193.1454	$193.15	$193.15	$193.10
Purchase #6	$185.80	12.110%	$208.3004	$208.30	$208.30	$208.30
Purchase #7	$174.98	7.544%	$188.1805	$188.18	$188.20	$188.20
7 purchase totals =	$1,100.56		$1,212.3293	$1,212.34	$1,212.35	$1,212.30