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	$59.48	13.418%	$67.461	$67.46	$67.45	$67.50
Purchase #2	$155.90	3.321%	$161.0774	$161.08	$161.10	$161.10
Purchase #3	$96.88	12.367%	$108.8611	$108.86	$108.85	$108.90
Purchase #4	$37.99	10.253%	$41.8851	$41.89	$41.90	$41.90
Purchase #5	$60.77	8.240%	$65.7774	$65.78	$65.80	$65.80
Purchase #6	$6.70	10.762%	$7.4211	$7.42	$7.40	$7.40
Purchase #7	$118.93	8.342%	$128.8511	$128.85	$128.85	$128.90
7 purchase totals =	$536.65		$581.3342	$581.34	$581.35	$581.50