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	$26.73	9.707%	$29.3247	$29.32	$29.30	$29.30
Purchase #2	$158.87	6.548%	$169.2728	$169.27	$169.25	$169.30
Purchase #3	$200.90	10.682%	$222.3601	$222.36	$222.35	$222.40
Purchase #4	$76.43	13.608%	$86.8306	$86.83	$86.85	$86.80
Purchase #5	$94.33	9.744%	$103.5215	$103.52	$103.50	$103.50
Purchase #6	$119.69	5.576%	$126.3639	$126.36	$126.35	$126.40
Purchase #7	$138.99	12.660%	$156.5861	$156.59	$156.60	$156.60
7 purchase totals =	$815.94		$894.2597	$894.25	$894.20	$894.30