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	$125.31	6.551%	$133.5191	$133.52	$133.50	$133.50
Purchase #2	$61.96	13.510%	$70.3308	$70.33	$70.35	$70.30
Purchase #3	$108.49	13.511%	$123.1481	$123.15	$123.15	$123.10
Purchase #4	$112.90	13.174%	$127.7734	$127.77	$127.75	$127.80
Purchase #5	$95.25	10.856%	$105.5903	$105.59	$105.60	$105.60
Purchase #6	$92.65	8.140%	$100.1917	$100.19	$100.20	$100.20
Purchase #7	$28.93	9.294%	$31.6188	$31.62	$31.60	$31.60
7 purchase totals =	$625.49		$692.1722	$692.17	$692.15	$692.10