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	$94.85	5.846%	$100.3949	$100.39	$100.40	$100.40
Purchase #2	$159.95	5.585%	$168.8832	$168.88	$168.90	$168.90
Purchase #3	$19.97	5.490%	$21.0664	$21.07	$21.05	$21.10
Purchase #4	$222.86	8.417%	$241.6181	$241.62	$241.60	$241.60
Purchase #5	$83.82	7.408%	$90.0294	$90.03	$90.05	$90.00
Purchase #6	$159.62	10.387%	$176.1997	$176.20	$176.20	$176.20
Purchase #7	$61.59	6.645%	$65.6827	$65.68	$65.70	$65.70
7 purchase totals =	$802.66		$863.8744	$863.87	$863.90	$863.90