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	$122.38	4.140%	$127.4465	$127.45	$127.45	$127.40
Purchase #2	$216.66	5.547%	$228.6781	$228.68	$228.70	$228.70
Purchase #3	$48.73	11.813%	$54.4865	$54.49	$54.50	$54.50
Purchase #4	$110.99	9.807%	$121.8748	$121.87	$121.85	$121.90
Purchase #5	$32.56	5.798%	$34.4478	$34.45	$34.45	$34.40
Purchase #6	$37.70	7.463%	$40.5136	$40.51	$40.50	$40.50
Purchase #7	$66.78	10.627%	$73.8767	$73.88	$73.90	$73.90
7 purchase totals =	$635.80		$681.3240	$681.33	$681.35	$681.30