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	$91.70	8.366%	$99.3716	$99.37	$99.35	$99.40
Purchase #2	$74.98	4.124%	$78.0722	$78.07	$78.05	$78.10
Purchase #3	$98.73	6.176%	$104.8276	$104.83	$104.85	$104.80
Purchase #4	$127.77	12.289%	$143.4717	$143.47	$143.45	$143.50
Purchase #5	$137.38	3.206%	$141.7844	$141.78	$141.80	$141.80
Purchase #6	$27.65	12.312%	$31.0543	$31.05	$31.05	$31.10
Purchase #7	$218.52	7.378%	$234.6424	$234.64	$234.65	$234.60
7 purchase totals =	$776.73		$833.2242	$833.21	$833.20	$833.30