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	$36.29	7.342%	$38.9544	$38.95	$38.95	$39.00
Purchase #2	$112.94	13.866%	$128.6003	$128.60	$128.60	$128.60
Purchase #3	$50.61	6.470%	$53.8845	$53.88	$53.90	$53.90
Purchase #4	$182.57	6.118%	$193.7396	$193.74	$193.75	$193.70
Purchase #5	$180.32	4.661%	$188.7247	$188.72	$188.70	$188.70
Purchase #6	$146.27	12.870%	$165.0949	$165.09	$165.10	$165.10
Purchase #7	$178.39	7.330%	$191.466	$191.47	$191.45	$191.50
7 purchase totals =	$887.39		$960.4644	$960.45	$960.45	$960.50