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	$54.52	11.711%	$60.9048	$60.90	$60.90	$60.90
Purchase #2	$209.76	10.136%	$231.0213	$231.02	$231.00	$231.00
Purchase #3	$101.47	11.821%	$113.4648	$113.46	$113.45	$113.50
Purchase #4	$210.93	7.175%	$226.0642	$226.06	$226.05	$226.10
Purchase #5	$161.46	8.176%	$174.661	$174.66	$174.65	$174.70
Purchase #6	$95.96	8.835%	$104.4381	$104.44	$104.45	$104.40
Purchase #7	$85.55	4.347%	$89.2689	$89.27	$89.25	$89.30
7 purchase totals =	$919.65		$999.8231	$999.81	$999.75	$999.90