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	$64.25	11.277%	$71.4955	$71.50	$71.50	$71.50
Purchase #2	$156.74	3.113%	$161.6193	$161.62	$161.60	$161.60
Purchase #3	$82.38	6.367%	$87.6251	$87.63	$87.65	$87.60
Purchase #4	$219.72	5.478%	$231.7563	$231.76	$231.75	$231.80
Purchase #5	$125.80	3.803%	$130.5842	$130.58	$130.60	$130.60
Purchase #6	$82.35	9.823%	$90.4392	$90.44	$90.45	$90.40
Purchase #7	$97.71	5.671%	$103.2511	$103.25	$103.25	$103.30
7 purchase totals =	$828.95		$876.7707	$876.78	$876.80	$876.80