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	$101.33	3.203%	$104.5756	$104.58	$104.60	$104.60
Purchase #2	$225.31	12.246%	$252.9015	$252.90	$252.90	$252.90
Purchase #3	$55.60	7.690%	$59.8756	$59.88	$59.90	$59.90
Purchase #4	$199.61	11.451%	$222.4673	$222.47	$222.45	$222.50
Purchase #5	$235.71	13.439%	$267.3871	$267.39	$267.40	$267.40
Purchase #6	$229.66	9.202%	$250.7933	$250.79	$250.80	$250.80
Purchase #7	$34.28	6.685%	$36.5716	$36.57	$36.55	$36.60
7 purchase totals =	$1,081.50		$1,194.5720	$1,194.58	$1,194.60	$1,194.70