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	$59.54	9.466%	$65.1761	$65.18	$65.20	$65.20
Purchase #2	$74.90	4.321%	$78.1364	$78.14	$78.15	$78.10
Purchase #3	$24.30	11.277%	$27.0403	$27.04	$27.05	$27.00
Purchase #4	$104.64	11.313%	$116.4779	$116.48	$116.50	$116.50
Purchase #5	$6.47	9.801%	$7.1041	$7.10	$7.10	$7.10
Purchase #6	$101.65	13.750%	$115.6269	$115.63	$115.65	$115.60
Purchase #7	$103.37	9.622%	$113.3163	$113.32	$113.30	$113.30
7 purchase totals =	$474.87		$522.8780	$522.89	$522.95	$522.80