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	$32.78	10.756%	$36.3058	$36.31	$36.30	$36.30
Purchase #2	$82.54	10.328%	$91.0647	$91.06	$91.05	$91.10
Purchase #3	$104.37	12.530%	$117.4476	$117.45	$117.45	$117.40
Purchase #4	$248.68	13.131%	$281.3342	$281.33	$281.35	$281.30
Purchase #5	$73.75	6.363%	$78.4427	$78.44	$78.45	$78.40
Purchase #6	$58.60	8.527%	$63.5968	$63.60	$63.60	$63.60
Purchase #7	$28.80	13.578%	$32.7105	$32.71	$32.70	$32.70
7 purchase totals =	$629.52		$700.9023	$700.90	$700.90	$700.80