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	$59.75	12.848%	$67.4267	$67.43	$67.45	$67.40
Purchase #2	$123.87	6.531%	$131.9599	$131.96	$131.95	$132.00
Purchase #3	$207.90	12.511%	$233.9104	$233.91	$233.90	$233.90
Purchase #4	$20.77	3.765%	$21.552	$21.55	$21.55	$21.60
Purchase #5	$128.83	9.571%	$141.1603	$141.16	$141.15	$141.20
Purchase #6	$99.88	6.372%	$106.2444	$106.24	$106.25	$106.20
Purchase #7	$178.57	5.197%	$187.8503	$187.85	$187.85	$187.90
7 purchase totals =	$819.57		$890.1040	$890.10	$890.10	$890.20