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	$76.57	5.177%	$80.534	$80.53	$80.55	$80.50
Purchase #2	$171.74	10.798%	$190.2845	$190.28	$190.30	$190.30
Purchase #3	$73.37	5.611%	$77.4868	$77.49	$77.50	$77.50
Purchase #4	$44.58	12.851%	$50.309	$50.31	$50.30	$50.30
Purchase #5	$247.55	6.828%	$264.4527	$264.45	$264.45	$264.50
Purchase #6	$70.39	3.256%	$72.6819	$72.68	$72.70	$72.70
Purchase #7	$187.70	10.177%	$206.8022	$206.80	$206.80	$206.80
7 purchase totals =	$871.90		$942.5511	$942.54	$942.60	$942.60