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	$39.43	3.106%	$40.6547	$40.65	$40.65	$40.70
Purchase #2	$155.80	5.684%	$164.6557	$164.66	$164.65	$164.70
Purchase #3	$37.74	7.571%	$40.5973	$40.60	$40.60	$40.60
Purchase #4	$188.41	10.321%	$207.8558	$207.86	$207.85	$207.90
Purchase #5	$20.39	6.479%	$21.7111	$21.71	$21.70	$21.70
Purchase #6	$40.63	4.522%	$42.4673	$42.47	$42.45	$42.50
Purchase #7	$128.52	7.248%	$137.8351	$137.84	$137.85	$137.80
7 purchase totals =	$610.92		$655.7770	$655.79	$655.75	$655.90