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	$30.89	9.641%	$33.8681	$33.87	$33.85	$33.90
Purchase #2	$127.98	9.796%	$140.5169	$140.52	$140.50	$140.50
Purchase #3	$96.42	4.256%	$100.5236	$100.52	$100.50	$100.50
Purchase #4	$63.32	4.338%	$66.0668	$66.07	$66.05	$66.10
Purchase #5	$140.71	9.152%	$153.5878	$153.59	$153.60	$153.60
Purchase #6	$132.86	9.273%	$145.1801	$145.18	$145.20	$145.20
Purchase #7	$7.42	3.689%	$7.6937	$7.69	$7.70	$7.70
7 purchase totals =	$599.60		$647.4370	$647.44	$647.40	$647.50