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	$18.59	9.326%	$20.3237	$20.32	$20.30	$20.30
Purchase #2	$241.93	12.437%	$272.0188	$272.02	$272.00	$272.00
Purchase #3	$220.52	11.642%	$246.1929	$246.19	$246.20	$246.20
Purchase #4	$172.79	8.547%	$187.5584	$187.56	$187.55	$187.60
Purchase #5	$234.56	12.350%	$263.5282	$263.53	$263.55	$263.50
Purchase #6	$17.47	5.343%	$18.4034	$18.40	$18.40	$18.40
Purchase #7	$65.69	3.337%	$67.8821	$67.88	$67.90	$67.90
7 purchase totals =	$971.55		$1,075.9075	$1,075.90	$1,075.90	$1,075.90