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	$124.97	12.706%	$140.8487	$140.85	$140.85	$140.80
Purchase #2	$31.38	4.509%	$32.7949	$32.79	$32.80	$32.80
Purchase #3	$101.85	9.367%	$111.3903	$111.39	$111.40	$111.40
Purchase #4	$152.92	9.128%	$166.8785	$166.88	$166.90	$166.90
Purchase #5	$160.41	8.363%	$173.8251	$173.83	$173.85	$173.80
Purchase #6	$91.67	4.147%	$95.4716	$95.47	$95.45	$95.50
Purchase #7	$96.47	5.617%	$101.8887	$101.89	$101.90	$101.90
7 purchase totals =	$759.67		$823.0978	$823.10	$823.15	$823.10