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	$162.68	10.459%	$179.6947	$179.69	$179.70	$179.70
Purchase #2	$69.40	4.735%	$72.6861	$72.69	$72.70	$72.70
Purchase #3	$20.69	5.779%	$21.8857	$21.89	$21.90	$21.90
Purchase #4	$138.66	9.324%	$151.5887	$151.59	$151.60	$151.60
Purchase #5	$112.67	8.756%	$122.5354	$122.54	$122.55	$122.50
Purchase #6	$99.85	12.329%	$112.1605	$112.16	$112.15	$112.20
Purchase #7	$170.62	4.774%	$178.7654	$178.77	$178.75	$178.80
7 purchase totals =	$774.57		$839.3165	$839.33	$839.35	$839.40