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	$5.76	8.273%	$6.2365	$6.24	$6.25	$6.20
Purchase #2	$240.33	13.390%	$272.5102	$272.51	$272.50	$272.50
Purchase #3	$174.72	3.269%	$180.4316	$180.43	$180.45	$180.40
Purchase #4	$99.88	11.538%	$111.4042	$111.40	$111.40	$111.40
Purchase #5	$183.54	12.250%	$206.0237	$206.02	$206.00	$206.00
Purchase #6	$87.64	9.501%	$95.9667	$95.97	$95.95	$96.00
Purchase #7	$108.48	7.752%	$116.8894	$116.89	$116.90	$116.90
7 purchase totals =	$900.35		$989.4623	$989.46	$989.45	$989.40