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	$19.53	8.799%	$21.2484	$21.25	$21.25	$21.20
Purchase #2	$156.69	4.354%	$163.5123	$163.51	$163.50	$163.50
Purchase #3	$140.39	8.487%	$152.3049	$152.30	$152.30	$152.30
Purchase #4	$116.47	10.296%	$128.4618	$128.46	$128.45	$128.50
Purchase #5	$121.53	13.720%	$138.2039	$138.20	$138.20	$138.20
Purchase #6	$137.43	9.794%	$150.8899	$150.89	$150.90	$150.90
Purchase #7	$30.49	5.741%	$32.2404	$32.24	$32.25	$32.20
7 purchase totals =	$722.53		$786.8616	$786.85	$786.85	$786.80