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	$172.43	9.534%	$188.8695	$188.87	$188.85	$188.90
Purchase #2	$141.34	10.460%	$156.1242	$156.12	$156.10	$156.10
Purchase #3	$157.70	9.441%	$172.5885	$172.59	$172.60	$172.60
Purchase #4	$98.43	4.874%	$103.2275	$103.23	$103.25	$103.20
Purchase #5	$33.29	3.414%	$34.4265	$34.43	$34.45	$34.40
Purchase #6	$25.45	13.811%	$28.9649	$28.96	$28.95	$29.00
Purchase #7	$161.86	6.249%	$171.9746	$171.97	$171.95	$172.00
7 purchase totals =	$790.50		$856.1757	$856.17	$856.15	$856.20