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	$122.78	12.127%	$137.6695	$137.67	$137.65	$137.70
Purchase #2	$141.70	7.629%	$152.5103	$152.51	$152.50	$152.50
Purchase #3	$112.75	9.277%	$123.2098	$123.21	$123.20	$123.20
Purchase #4	$64.39	11.552%	$71.8283	$71.83	$71.85	$71.80
Purchase #5	$137.66	7.553%	$148.0575	$148.06	$148.05	$148.10
Purchase #6	$160.30	13.777%	$182.3845	$182.38	$182.40	$182.40
Purchase #7	$178.59	4.394%	$186.4372	$186.44	$186.45	$186.40
7 purchase totals =	$918.17		$1,002.0971	$1,002.10	$1,002.10	$1,002.10