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	$194.31	12.114%	$217.8487	$217.85	$217.85	$217.80
Purchase #2	$243.96	11.443%	$271.8763	$271.88	$271.90	$271.90
Purchase #3	$225.59	9.701%	$247.4745	$247.47	$247.45	$247.50
Purchase #4	$99.47	13.746%	$113.1431	$113.14	$113.15	$113.10
Purchase #5	$131.85	7.382%	$141.5832	$141.58	$141.60	$141.60
Purchase #6	$45.68	3.547%	$47.3003	$47.30	$47.30	$47.30
Purchase #7	$135.41	11.724%	$151.2855	$151.29	$151.30	$151.30
7 purchase totals =	$1,076.27		$1,190.5116	$1,190.51	$1,190.55	$1,190.50