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	$49.37	10.576%	$54.5914	$54.59	$54.60	$54.60
Purchase #2	$92.43	12.636%	$104.1095	$104.11	$104.10	$104.10
Purchase #3	$177.70	10.634%	$196.5966	$196.60	$196.60	$196.60
Purchase #4	$67.38	5.507%	$71.0906	$71.09	$71.10	$71.10
Purchase #5	$118.27	5.491%	$124.7642	$124.76	$124.75	$124.80
Purchase #6	$71.88	11.368%	$80.0513	$80.05	$80.05	$80.10
Purchase #7	$168.38	12.515%	$189.4528	$189.45	$189.45	$189.50
7 purchase totals =	$745.41		$820.6564	$820.65	$820.65	$820.80