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	$226.97	6.660%	$242.0862	$242.09	$242.10	$242.10
Purchase #2	$128.67	12.263%	$144.4488	$144.45	$144.45	$144.40
Purchase #3	$48.51	9.472%	$53.1049	$53.10	$53.10	$53.10
Purchase #4	$205.51	5.210%	$216.2171	$216.22	$216.20	$216.20
Purchase #5	$218.47	5.113%	$229.6404	$229.64	$229.65	$229.60
Purchase #6	$246.25	3.716%	$255.4007	$255.40	$255.40	$255.40
Purchase #7	$125.68	4.579%	$131.4349	$131.43	$131.45	$131.40
7 purchase totals =	$1,200.06		$1,272.3330	$1,272.33	$1,272.35	$1,272.20