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	$14.26	5.541%	$15.0501	$15.05	$15.05	$15.10
Purchase #2	$86.60	4.299%	$90.3229	$90.32	$90.30	$90.30
Purchase #3	$77.87	3.230%	$80.3852	$80.39	$80.40	$80.40
Purchase #4	$93.71	9.197%	$102.3285	$102.33	$102.35	$102.30
Purchase #5	$14.76	10.128%	$16.2549	$16.25	$16.25	$16.30
Purchase #6	$174.91	12.322%	$196.4624	$196.46	$196.45	$196.50
Purchase #7	$118.34	13.870%	$134.7538	$134.75	$134.75	$134.80
7 purchase totals =	$580.45		$635.5578	$635.55	$635.55	$635.70