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	$121.83	12.860%	$137.4973	$137.50	$137.50	$137.50
Purchase #2	$33.40	3.367%	$34.5246	$34.52	$34.50	$34.50
Purchase #3	$20.60	8.545%	$22.3603	$22.36	$22.35	$22.40
Purchase #4	$91.92	8.207%	$99.4639	$99.46	$99.45	$99.50
Purchase #5	$146.66	3.691%	$152.0732	$152.07	$152.05	$152.10
Purchase #6	$132.89	7.740%	$143.1757	$143.18	$143.20	$143.20
Purchase #7	$67.87	12.210%	$76.1569	$76.16	$76.15	$76.20
7 purchase totals =	$615.17		$665.2519	$665.25	$665.20	$665.40