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	$246.83	6.772%	$263.5453	$263.55	$263.55	$263.50
Purchase #2	$35.73	13.744%	$40.6407	$40.64	$40.65	$40.60
Purchase #3	$24.31	5.666%	$25.6874	$25.69	$25.70	$25.70
Purchase #4	$14.77	5.753%	$15.6197	$15.62	$15.60	$15.60
Purchase #5	$67.56	7.795%	$72.8263	$72.83	$72.85	$72.80
Purchase #6	$133.46	4.697%	$139.7286	$139.73	$139.75	$139.70
Purchase #7	$249.51	5.228%	$262.5544	$262.55	$262.55	$262.60
7 purchase totals =	$772.17		$820.6024	$820.61	$820.65	$820.50