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	$70.80	11.129%	$78.6793	$78.68	$78.70	$78.70
Purchase #2	$208.80	6.603%	$222.5871	$222.59	$222.60	$222.60
Purchase #3	$29.95	12.493%	$33.6917	$33.69	$33.70	$33.70
Purchase #4	$24.65	10.165%	$27.1557	$27.16	$27.15	$27.20
Purchase #5	$102.55	13.459%	$116.3522	$116.35	$116.35	$116.40
Purchase #6	$29.77	11.843%	$33.2957	$33.30	$33.30	$33.30
Purchase #7	$239.60	4.764%	$251.0145	$251.01	$251.00	$251.00
7 purchase totals =	$706.12		$762.7762	$762.78	$762.80	$762.90