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	$223.61	6.162%	$237.3888	$237.39	$237.40	$237.40
Purchase #2	$214.87	6.473%	$228.7785	$228.78	$228.80	$228.80
Purchase #3	$91.35	8.225%	$98.8635	$98.86	$98.85	$98.90
Purchase #4	$97.79	9.353%	$106.9363	$106.94	$106.95	$106.90
Purchase #5	$85.55	11.705%	$95.5636	$95.56	$95.55	$95.60
Purchase #6	$95.56	7.189%	$102.4298	$102.43	$102.45	$102.40
Purchase #7	$211.91	13.809%	$241.1727	$241.17	$241.15	$241.20
7 purchase totals =	$1,020.64		$1,111.1332	$1,111.13	$1,111.15	$1,111.20