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	$80.99	6.422%	$86.1912	$86.19	$86.20	$86.20
Purchase #2	$21.36	10.392%	$23.5797	$23.58	$23.60	$23.60
Purchase #3	$111.89	5.584%	$118.1379	$118.14	$118.15	$118.10
Purchase #4	$233.78	9.717%	$256.4964	$256.50	$256.50	$256.50
Purchase #5	$39.83	5.397%	$41.9796	$41.98	$42.00	$42.00
Purchase #6	$37.55	7.812%	$40.4834	$40.48	$40.50	$40.50
Purchase #7	$75.85	9.211%	$82.8365	$82.84	$82.85	$82.80
7 purchase totals =	$601.25		$649.7047	$649.71	$649.80	$649.70