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	$128.90	8.495%	$139.8501	$139.85	$139.85	$139.90
Purchase #2	$130.33	7.349%	$139.908	$139.91	$139.90	$139.90
Purchase #3	$108.72	3.816%	$112.8688	$112.87	$112.85	$112.90
Purchase #4	$171.29	4.272%	$178.6075	$178.61	$178.60	$178.60
Purchase #5	$146.48	6.737%	$156.3484	$156.35	$156.35	$156.30
Purchase #6	$148.43	6.714%	$158.3956	$158.40	$158.40	$158.40
Purchase #7	$120.48	9.731%	$132.2039	$132.20	$132.20	$132.20
7 purchase totals =	$954.63		$1,018.1823	$1,018.19	$1,018.15	$1,018.20