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	$174.97	10.581%	$193.4836	$193.48	$193.50	$193.50
Purchase #2	$38.82	6.624%	$41.3914	$41.39	$41.40	$41.40
Purchase #3	$87.82	13.202%	$99.414	$99.41	$99.40	$99.40
Purchase #4	$143.88	5.675%	$152.0452	$152.05	$152.05	$152.00
Purchase #5	$222.39	13.703%	$252.8641	$252.86	$252.85	$252.90
Purchase #6	$82.61	9.116%	$90.1407	$90.14	$90.15	$90.10
Purchase #7	$38.68	8.332%	$41.9028	$41.90	$41.90	$41.90
7 purchase totals =	$789.17		$871.2418	$871.23	$871.25	$871.20