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	$245.76	11.673%	$274.4476	$274.45	$274.45	$274.40
Purchase #2	$68.46	3.393%	$70.7828	$70.78	$70.80	$70.80
Purchase #3	$172.77	7.318%	$185.4133	$185.41	$185.40	$185.40
Purchase #4	$9.72	13.223%	$11.0053	$11.01	$11.00	$11.00
Purchase #5	$140.60	13.463%	$159.529	$159.53	$159.55	$159.50
Purchase #6	$40.52	12.686%	$45.6604	$45.66	$45.65	$45.70
Purchase #7	$180.25	10.262%	$198.7473	$198.75	$198.75	$198.70
7 purchase totals =	$858.08		$945.5857	$945.59	$945.60	$945.50