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	$46.46	12.793%	$52.4036	$52.40	$52.40	$52.40
Purchase #2	$73.92	12.122%	$82.8806	$82.88	$82.90	$82.90
Purchase #3	$125.43	13.620%	$142.5136	$142.51	$142.50	$142.50
Purchase #4	$148.92	6.345%	$158.369	$158.37	$158.35	$158.40
Purchase #5	$99.25	8.634%	$107.8192	$107.82	$107.80	$107.80
Purchase #6	$36.73	8.516%	$39.8579	$39.86	$39.85	$39.90
Purchase #7	$17.99	8.841%	$19.5805	$19.58	$19.60	$19.60
7 purchase totals =	$548.70		$603.4244	$603.42	$603.40	$603.50