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	$104.73	6.376%	$111.4076	$111.41	$111.40	$111.40
Purchase #2	$232.66	4.574%	$243.3019	$243.30	$243.30	$243.30
Purchase #3	$178.53	5.244%	$187.8921	$187.89	$187.90	$187.90
Purchase #4	$45.42	7.729%	$48.9305	$48.93	$48.95	$48.90
Purchase #5	$242.93	8.184%	$262.8114	$262.81	$262.80	$262.80
Purchase #6	$184.67	4.419%	$192.8306	$192.83	$192.85	$192.80
Purchase #7	$103.53	4.522%	$108.2116	$108.21	$108.20	$108.20
7 purchase totals =	$1,092.47		$1,155.3857	$1,155.38	$1,155.40	$1,155.30