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	$19.72	9.391%	$21.5719	$21.57	$21.55	$21.60
Purchase #2	$204.48	12.544%	$230.13	$230.13	$230.15	$230.10
Purchase #3	$90.60	4.200%	$94.4052	$94.41	$94.40	$94.40
Purchase #4	$48.53	5.741%	$51.3161	$51.32	$51.30	$51.30
Purchase #5	$232.55	13.269%	$263.4071	$263.41	$263.40	$263.40
Purchase #6	$145.34	12.116%	$162.9494	$162.95	$162.95	$162.90
Purchase #7	$234.93	8.759%	$255.5075	$255.51	$255.50	$255.50
7 purchase totals =	$976.15		$1,079.2872	$1,079.30	$1,079.25	$1,079.20