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	$34.74	10.571%	$38.4124	$38.41	$38.40	$38.40
Purchase #2	$247.90	7.831%	$267.313	$267.31	$267.30	$267.30
Purchase #3	$38.83	4.819%	$40.7012	$40.70	$40.70	$40.70
Purchase #4	$177.83	12.599%	$200.2348	$200.23	$200.25	$200.20
Purchase #5	$166.89	13.597%	$189.582	$189.58	$189.60	$189.60
Purchase #6	$94.35	11.562%	$105.2587	$105.26	$105.25	$105.30
Purchase #7	$83.62	8.287%	$90.5496	$90.55	$90.55	$90.50
7 purchase totals =	$844.16		$932.0517	$932.04	$932.05	$932.00