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	$87.89	3.418%	$90.8941	$90.89	$90.90	$90.90
Purchase #2	$156.55	12.174%	$175.6084	$175.61	$175.60	$175.60
Purchase #3	$37.67	12.196%	$42.2642	$42.26	$42.25	$42.30
Purchase #4	$210.45	3.395%	$217.5948	$217.59	$217.60	$217.60
Purchase #5	$26.99	10.301%	$29.7702	$29.77	$29.75	$29.80
Purchase #6	$96.53	9.874%	$106.0614	$106.06	$106.05	$106.10
Purchase #7	$110.32	12.478%	$124.0857	$124.09	$124.10	$124.10
7 purchase totals =	$726.40		$786.2788	$786.27	$786.25	$786.40