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	$127.71	7.146%	$136.8362	$136.84	$136.85	$136.80
Purchase #2	$166.54	3.730%	$172.7519	$172.75	$172.75	$172.80
Purchase #3	$20.25	5.263%	$21.3158	$21.32	$21.30	$21.30
Purchase #4	$126.45	5.166%	$132.9824	$132.98	$133.00	$133.00
Purchase #5	$81.74	10.476%	$90.3031	$90.30	$90.30	$90.30
Purchase #6	$221.49	8.715%	$240.7929	$240.79	$240.80	$240.80
Purchase #7	$15.58	12.562%	$17.5372	$17.54	$17.55	$17.50
7 purchase totals =	$759.76		$812.5195	$812.52	$812.55	$812.50