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	$22.77	7.660%	$24.5142	$24.51	$24.50	$24.50
Purchase #2	$118.56	4.117%	$123.4411	$123.44	$123.45	$123.40
Purchase #3	$169.62	11.765%	$189.5758	$189.58	$189.60	$189.60
Purchase #4	$48.72	11.801%	$54.4694	$54.47	$54.45	$54.50
Purchase #5	$94.52	5.230%	$99.4634	$99.46	$99.45	$99.50
Purchase #6	$228.63	3.323%	$236.2274	$236.23	$236.25	$236.20
Purchase #7	$126.86	7.468%	$136.3339	$136.33	$136.35	$136.30
7 purchase totals =	$809.68		$864.0252	$864.02	$864.05	$864.00