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	$159.86	8.516%	$173.4737	$173.47	$173.45	$173.50
Purchase #2	$171.48	12.110%	$192.2462	$192.25	$192.25	$192.20
Purchase #3	$69.80	4.509%	$72.9473	$72.95	$72.95	$72.90
Purchase #4	$141.25	3.279%	$145.8816	$145.88	$145.90	$145.90
Purchase #5	$36.29	13.314%	$41.1217	$41.12	$41.10	$41.10
Purchase #6	$150.90	5.354%	$158.9792	$158.98	$159.00	$159.00
Purchase #7	$96.77	7.852%	$104.3684	$104.37	$104.35	$104.40
7 purchase totals =	$826.35		$889.0181	$889.02	$889.00	$889.00