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	$87.48	13.210%	$99.0361	$99.04	$99.05	$99.00
Purchase #2	$43.55	10.727%	$48.2216	$48.22	$48.20	$48.20
Purchase #3	$110.32	5.286%	$116.1515	$116.15	$116.15	$116.20
Purchase #4	$215.56	7.594%	$231.9296	$231.93	$231.95	$231.90
Purchase #5	$219.65	6.250%	$233.3781	$233.38	$233.40	$233.40
Purchase #6	$30.38	8.113%	$32.8447	$32.84	$32.85	$32.80
Purchase #7	$137.57	13.675%	$156.3827	$156.38	$156.40	$156.40
7 purchase totals =	$844.51		$917.9443	$917.94	$918.00	$917.90