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	$33.38	13.706%	$37.9551	$37.96	$37.95	$38.00
Purchase #2	$77.58	6.426%	$82.5653	$82.57	$82.55	$82.60
Purchase #3	$208.30	10.190%	$229.5258	$229.53	$229.55	$229.50
Purchase #4	$176.34	5.314%	$185.7107	$185.71	$185.70	$185.70
Purchase #5	$166.70	10.854%	$184.7936	$184.79	$184.80	$184.80
Purchase #6	$122.79	4.109%	$127.8354	$127.84	$127.85	$127.80
Purchase #7	$113.65	6.831%	$121.4134	$121.41	$121.40	$121.40
7 purchase totals =	$898.74		$969.7993	$969.81	$969.80	$969.80