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	$24.47	11.417%	$27.2637	$27.26	$27.25	$27.30
Purchase #2	$82.38	3.287%	$85.0878	$85.09	$85.10	$85.10
Purchase #3	$52.48	10.627%	$58.057	$58.06	$58.05	$58.10
Purchase #4	$99.37	4.607%	$103.948	$103.95	$103.95	$103.90
Purchase #5	$133.45	7.647%	$143.6549	$143.65	$143.65	$143.70
Purchase #6	$153.56	8.712%	$166.9381	$166.94	$166.95	$166.90
Purchase #7	$63.45	6.417%	$67.5216	$67.52	$67.50	$67.50
7 purchase totals =	$609.16		$652.4711	$652.47	$652.45	$652.50