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	$160.31	4.325%	$167.2434	$167.24	$167.25	$167.20
Purchase #2	$227.38	3.257%	$234.7858	$234.79	$234.80	$234.80
Purchase #3	$150.89	11.332%	$167.9889	$167.99	$168.00	$168.00
Purchase #4	$165.84	4.147%	$172.7174	$172.72	$172.70	$172.70
Purchase #5	$231.28	12.251%	$259.6141	$259.61	$259.60	$259.60
Purchase #6	$78.83	7.572%	$84.799	$84.80	$84.80	$84.80
Purchase #7	$75.56	3.603%	$78.2824	$78.28	$78.30	$78.30
7 purchase totals =	$1,090.09		$1,165.4310	$1,165.43	$1,165.45	$1,165.40