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	$249.56	9.609%	$273.5402	$273.54	$273.55	$273.50
Purchase #2	$225.65	13.311%	$255.6863	$255.69	$255.70	$255.70
Purchase #3	$225.97	10.502%	$249.7014	$249.70	$249.70	$249.70
Purchase #4	$130.51	9.760%	$143.2478	$143.25	$143.25	$143.20
Purchase #5	$129.54	10.734%	$143.4448	$143.44	$143.45	$143.40
Purchase #6	$64.92	10.612%	$71.8093	$71.81	$71.80	$71.80
Purchase #7	$170.35	9.113%	$185.874	$185.87	$185.85	$185.90
7 purchase totals =	$1,196.50		$1,323.3038	$1,323.30	$1,323.30	$1,323.20