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	$80.25	4.192%	$83.6141	$83.61	$83.60	$83.60
Purchase #2	$124.53	13.273%	$141.0589	$141.06	$141.05	$141.10
Purchase #3	$205.43	5.833%	$217.4127	$217.41	$217.40	$217.40
Purchase #4	$25.44	10.781%	$28.1827	$28.18	$28.20	$28.20
Purchase #5	$71.28	12.716%	$80.344	$80.34	$80.35	$80.30
Purchase #6	$54.75	6.740%	$58.4402	$58.44	$58.45	$58.40
Purchase #7	$156.82	6.825%	$167.523	$167.52	$167.50	$167.50
7 purchase totals =	$718.50		$776.5756	$776.56	$776.55	$776.50