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	$244.97	10.857%	$271.5664	$271.57	$271.55	$271.60
Purchase #2	$139.60	6.382%	$148.5093	$148.51	$148.50	$148.50
Purchase #3	$95.51	9.566%	$104.6465	$104.65	$104.65	$104.60
Purchase #4	$51.68	6.555%	$55.0676	$55.07	$55.05	$55.10
Purchase #5	$240.32	11.683%	$268.3966	$268.40	$268.40	$268.40
Purchase #6	$245.33	4.146%	$255.5014	$255.50	$255.50	$255.50
Purchase #7	$182.73	7.824%	$197.0268	$197.03	$197.05	$197.00
7 purchase totals =	$1,200.14		$1,300.7146	$1,300.73	$1,300.70	$1,300.70