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	$202.85	9.178%	$221.4676	$221.47	$221.45	$221.50
Purchase #2	$170.94	11.187%	$190.0631	$190.06	$190.05	$190.10
Purchase #3	$76.80	11.455%	$85.5974	$85.60	$85.60	$85.60
Purchase #4	$205.73	8.244%	$222.6904	$222.69	$222.70	$222.70
Purchase #5	$94.35	8.549%	$102.416	$102.42	$102.40	$102.40
Purchase #6	$26.82	6.650%	$28.6035	$28.60	$28.60	$28.60
Purchase #7	$68.42	4.196%	$71.2909	$71.29	$71.30	$71.30
7 purchase totals =	$845.91		$922.1289	$922.13	$922.10	$922.20