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	$141.89	6.323%	$150.8617	$150.86	$150.85	$150.90
Purchase #2	$194.88	11.816%	$217.907	$217.91	$217.90	$217.90
Purchase #3	$137.56	9.296%	$150.3476	$150.35	$150.35	$150.30
Purchase #4	$133.55	6.161%	$141.778	$141.78	$141.80	$141.80
Purchase #5	$29.46	9.158%	$32.1579	$32.16	$32.15	$32.20
Purchase #6	$196.51	9.321%	$214.8267	$214.83	$214.85	$214.80
Purchase #7	$63.49	4.413%	$66.2918	$66.29	$66.30	$66.30
7 purchase totals =	$897.34		$974.1707	$974.18	$974.20	$974.20