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	$125.59	8.420%	$136.1647	$136.16	$136.15	$136.20
Purchase #2	$148.41	9.480%	$162.4793	$162.48	$162.50	$162.50
Purchase #3	$50.51	7.187%	$54.1402	$54.14	$54.15	$54.10
Purchase #4	$48.88	10.287%	$53.9083	$53.91	$53.90	$53.90
Purchase #5	$104.36	6.756%	$111.4106	$111.41	$111.40	$111.40
Purchase #6	$138.92	10.458%	$153.4483	$153.45	$153.45	$153.40
Purchase #7	$9.33	11.675%	$10.4193	$10.42	$10.40	$10.40
7 purchase totals =	$626.00		$681.9707	$681.97	$681.95	$681.90