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	$139.80	11.861%	$156.3817	$156.38	$156.40	$156.40
Purchase #2	$104.32	4.748%	$109.2731	$109.27	$109.25	$109.30
Purchase #3	$43.83	11.806%	$49.0046	$49.00	$49.00	$49.00
Purchase #4	$86.28	7.658%	$92.8873	$92.89	$92.90	$92.90
Purchase #5	$46.56	10.700%	$51.5419	$51.54	$51.55	$51.50
Purchase #6	$7.83	12.339%	$8.7961	$8.80	$8.80	$8.80
Purchase #7	$112.88	11.835%	$126.2393	$126.24	$126.25	$126.20
7 purchase totals =	$541.50		$594.1240	$594.12	$594.15	$594.10