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	$38.83	11.574%	$43.3242	$43.32	$43.30	$43.30
Purchase #2	$28.97	7.492%	$31.1404	$31.14	$31.15	$31.10
Purchase #3	$16.45	11.859%	$18.4008	$18.40	$18.40	$18.40
Purchase #4	$96.45	4.677%	$100.961	$100.96	$100.95	$101.00
Purchase #5	$163.95	13.122%	$185.4635	$185.46	$185.45	$185.50
Purchase #6	$121.56	12.264%	$136.4681	$136.47	$136.45	$136.50
Purchase #7	$153.66	5.743%	$162.4847	$162.48	$162.50	$162.50
7 purchase totals =	$619.87		$678.2427	$678.23	$678.20	$678.30