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	$104.93	4.174%	$109.3098	$109.31	$109.30	$109.30
Purchase #2	$148.83	10.778%	$164.8709	$164.87	$164.85	$164.90
Purchase #3	$70.59	10.510%	$78.009	$78.01	$78.00	$78.00
Purchase #4	$250.42	11.445%	$279.0806	$279.08	$279.10	$279.10
Purchase #5	$25.38	3.368%	$26.2348	$26.23	$26.25	$26.20
Purchase #6	$165.58	10.742%	$183.3666	$183.37	$183.35	$183.40
Purchase #7	$113.71	11.340%	$126.6047	$126.60	$126.60	$126.60
7 purchase totals =	$879.44		$967.4764	$967.47	$967.45	$967.50