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	$109.98	12.396%	$123.6131	$123.61	$123.60	$123.60
Purchase #2	$135.61	9.337%	$148.2719	$148.27	$148.25	$148.30
Purchase #3	$55.70	12.409%	$62.6118	$62.61	$62.60	$62.60
Purchase #4	$88.25	8.170%	$95.46	$95.46	$95.45	$95.50
Purchase #5	$42.62	4.205%	$44.4122	$44.41	$44.40	$44.40
Purchase #6	$160.82	8.643%	$174.7197	$174.72	$174.70	$174.70
Purchase #7	$233.69	6.806%	$249.5949	$249.59	$249.60	$249.60
7 purchase totals =	$826.67		$898.6836	$898.67	$898.60	$898.70