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	$73.78	8.558%	$80.0941	$80.09	$80.10	$80.10
Purchase #2	$100.58	12.183%	$112.8337	$112.83	$112.85	$112.80
Purchase #3	$135.28	6.403%	$143.942	$143.94	$143.95	$143.90
Purchase #4	$21.45	11.650%	$23.9489	$23.95	$23.95	$23.90
Purchase #5	$179.96	6.510%	$191.6754	$191.68	$191.70	$191.70
Purchase #6	$47.39	6.804%	$50.6144	$50.61	$50.60	$50.60
Purchase #7	$174.71	6.176%	$185.5001	$185.50	$185.50	$185.50
7 purchase totals =	$733.15		$788.6086	$788.60	$788.65	$788.50