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	$104.88	3.146%	$108.1795	$108.18	$108.20	$108.20
Purchase #2	$79.50	13.391%	$90.1458	$90.15	$90.15	$90.10
Purchase #3	$119.26	3.534%	$123.4746	$123.47	$123.45	$123.50
Purchase #4	$111.69	8.691%	$121.397	$121.40	$121.40	$121.40
Purchase #5	$118.67	10.606%	$131.2561	$131.26	$131.25	$131.30
Purchase #6	$49.83	13.650%	$56.6318	$56.63	$56.65	$56.60
Purchase #7	$30.49	5.817%	$32.2636	$32.26	$32.25	$32.30
7 purchase totals =	$614.32		$663.3484	$663.35	$663.35	$663.40