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	$92.71	5.151%	$97.4855	$97.49	$97.50	$97.50
Purchase #2	$114.77	3.669%	$118.9809	$118.98	$119.00	$119.00
Purchase #3	$143.82	8.574%	$156.1511	$156.15	$156.15	$156.20
Purchase #4	$31.29	5.778%	$33.0979	$33.10	$33.10	$33.10
Purchase #5	$92.75	4.513%	$96.9358	$96.94	$96.95	$96.90
Purchase #6	$20.32	7.532%	$21.8505	$21.85	$21.85	$21.90
Purchase #7	$92.49	7.577%	$99.498	$99.50	$99.50	$99.50
7 purchase totals =	$588.15		$623.9997	$624.01	$624.05	$624.10