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	$150.84	6.339%	$160.4017	$160.40	$160.40	$160.40
Purchase #2	$32.38	4.104%	$33.7089	$33.71	$33.70	$33.70
Purchase #3	$116.43	9.510%	$127.5025	$127.50	$127.50	$127.50
Purchase #4	$127.76	8.802%	$139.0054	$139.01	$139.00	$139.00
Purchase #5	$217.77	7.680%	$234.4947	$234.49	$234.50	$234.50
Purchase #6	$136.88	8.453%	$148.4505	$148.45	$148.45	$148.50
Purchase #7	$117.96	12.279%	$132.4443	$132.44	$132.45	$132.40
7 purchase totals =	$900.02		$976.0080	$976.00	$976.00	$976.00