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	$92.38	6.320%	$98.2184	$98.22	$98.20	$98.20
Purchase #2	$54.47	9.148%	$59.4529	$59.45	$59.45	$59.50
Purchase #3	$206.56	6.788%	$220.5813	$220.58	$220.60	$220.60
Purchase #4	$117.48	11.208%	$130.6472	$130.65	$130.65	$130.60
Purchase #5	$101.96	13.872%	$116.1039	$116.10	$116.10	$116.10
Purchase #6	$120.50	13.267%	$136.4867	$136.49	$136.50	$136.50
Purchase #7	$15.58	12.443%	$17.5186	$17.52	$17.50	$17.50
7 purchase totals =	$708.93		$779.0090	$779.01	$779.00	$779.00