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	$249.33	9.484%	$272.9765	$272.98	$273.00	$273.00
Purchase #2	$126.66	9.194%	$138.3051	$138.31	$138.30	$138.30
Purchase #3	$78.83	5.665%	$83.2957	$83.30	$83.30	$83.30
Purchase #4	$36.73	4.734%	$38.4688	$38.47	$38.45	$38.50
Purchase #5	$80.87	13.349%	$91.6653	$91.67	$91.65	$91.70
Purchase #6	$158.89	8.306%	$172.0874	$172.09	$172.10	$172.10
Purchase #7	$211.82	4.829%	$222.0488	$222.05	$222.05	$222.00
7 purchase totals =	$943.13		$1,018.8476	$1,018.87	$1,018.85	$1,018.90