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	$23.83	3.149%	$24.5804	$24.58	$24.60	$24.60
Purchase #2	$100.70	7.349%	$108.1004	$108.10	$108.10	$108.10
Purchase #3	$149.42	13.664%	$169.8367	$169.84	$169.85	$169.80
Purchase #4	$243.92	13.807%	$277.598	$277.60	$277.60	$277.60
Purchase #5	$91.53	8.289%	$99.1169	$99.12	$99.10	$99.10
Purchase #6	$237.60	7.325%	$255.0042	$255.00	$255.00	$255.00
Purchase #7	$64.33	4.505%	$67.2281	$67.23	$67.25	$67.20
7 purchase totals =	$911.33		$1,001.4647	$1,001.47	$1,001.50	$1,001.40