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	$63.78	11.504%	$71.1173	$71.12	$71.10	$71.10
Purchase #2	$203.31	5.660%	$214.8173	$214.82	$214.80	$214.80
Purchase #3	$96.57	9.268%	$105.5201	$105.52	$105.50	$105.50
Purchase #4	$95.90	8.193%	$103.7571	$103.76	$103.75	$103.80
Purchase #5	$176.99	10.704%	$195.935	$195.94	$195.95	$195.90
Purchase #6	$15.77	10.442%	$17.4167	$17.42	$17.40	$17.40
Purchase #7	$105.78	13.803%	$120.3808	$120.38	$120.40	$120.40
7 purchase totals =	$758.10		$828.9443	$828.96	$828.90	$828.90