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	$19.66	8.855%	$21.4009	$21.40	$21.40	$21.40
Purchase #2	$159.53	4.870%	$167.2991	$167.30	$167.30	$167.30
Purchase #3	$63.86	3.574%	$66.1424	$66.14	$66.15	$66.10
Purchase #4	$38.82	8.449%	$42.0999	$42.10	$42.10	$42.10
Purchase #5	$134.64	4.661%	$140.9156	$140.92	$140.90	$140.90
Purchase #6	$99.26	12.457%	$111.6248	$111.62	$111.60	$111.60
Purchase #7	$54.67	8.211%	$59.159	$59.16	$59.15	$59.20
7 purchase totals =	$570.44		$608.6417	$608.64	$608.60	$608.60