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	$245.29	10.257%	$270.4494	$270.45	$270.45	$270.40
Purchase #2	$158.70	12.358%	$178.3121	$178.31	$178.30	$178.30
Purchase #3	$123.67	13.256%	$140.0637	$140.06	$140.05	$140.10
Purchase #4	$154.71	5.320%	$162.9406	$162.94	$162.95	$162.90
Purchase #5	$43.33	7.454%	$46.5598	$46.56	$46.55	$46.60
Purchase #6	$55.36	12.813%	$62.4533	$62.45	$62.45	$62.50
Purchase #7	$218.46	9.455%	$239.1154	$239.12	$239.10	$239.10
7 purchase totals =	$999.52		$1,099.8943	$1,099.89	$1,099.85	$1,099.90