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	$8.50	4.541%	$8.886	$8.89	$8.90	$8.90
Purchase #2	$127.79	3.451%	$132.2	$132.20	$132.20	$132.20
Purchase #3	$116.99	12.440%	$131.5436	$131.54	$131.55	$131.50
Purchase #4	$170.36	5.169%	$179.1659	$179.17	$179.15	$179.20
Purchase #5	$124.30	11.483%	$138.5734	$138.57	$138.55	$138.60
Purchase #6	$77.76	6.622%	$82.9093	$82.91	$82.90	$82.90
Purchase #7	$78.80	8.349%	$85.379	$85.38	$85.40	$85.40
7 purchase totals =	$704.50		$758.6572	$758.66	$758.65	$758.70