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	$62.80	5.364%	$66.1686	$66.17	$66.15	$66.20
Purchase #2	$178.42	12.572%	$200.851	$200.85	$200.85	$200.90
Purchase #3	$22.72	7.665%	$24.4615	$24.46	$24.45	$24.50
Purchase #4	$87.78	11.747%	$98.0915	$98.09	$98.10	$98.10
Purchase #5	$92.28	12.130%	$103.4736	$103.47	$103.45	$103.50
Purchase #6	$38.88	13.530%	$44.1405	$44.14	$44.15	$44.10
Purchase #7	$242.34	10.872%	$268.6872	$268.69	$268.70	$268.70
7 purchase totals =	$725.22		$805.8739	$805.87	$805.85	$806.00