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	$249.31	7.297%	$267.5022	$267.50	$267.50	$267.50
Purchase #2	$103.89	11.832%	$116.1823	$116.18	$116.20	$116.20
Purchase #3	$175.74	8.730%	$191.0821	$191.08	$191.10	$191.10
Purchase #4	$180.59	6.633%	$192.5685	$192.57	$192.55	$192.60
Purchase #5	$139.62	6.367%	$148.5096	$148.51	$148.50	$148.50
Purchase #6	$31.30	9.530%	$34.2829	$34.28	$34.30	$34.30
Purchase #7	$48.77	11.530%	$54.3932	$54.39	$54.40	$54.40
7 purchase totals =	$929.22		$1,004.5208	$1,004.51	$1,004.55	$1,004.60