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	$29.72	9.626%	$32.5808	$32.58	$32.60	$32.60
Purchase #2	$172.44	6.857%	$184.2642	$184.26	$184.25	$184.30
Purchase #3	$88.41	4.496%	$92.3849	$92.38	$92.40	$92.40
Purchase #4	$32.29	7.313%	$34.6514	$34.65	$34.65	$34.70
Purchase #5	$35.32	6.342%	$37.56	$37.56	$37.55	$37.60
Purchase #6	$20.52	6.745%	$21.9041	$21.90	$21.90	$21.90
Purchase #7	$172.37	5.769%	$182.314	$182.31	$182.30	$182.30
7 purchase totals =	$551.07		$585.6594	$585.64	$585.65	$585.80