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	$242.29	9.172%	$264.5128	$264.51	$264.50	$264.50
Purchase #2	$113.64	3.323%	$117.4163	$117.42	$117.40	$117.40
Purchase #3	$78.46	8.870%	$85.4194	$85.42	$85.40	$85.40
Purchase #4	$45.35	10.340%	$50.0392	$50.04	$50.05	$50.00
Purchase #5	$239.93	13.547%	$272.4333	$272.43	$272.45	$272.40
Purchase #6	$46.56	12.661%	$52.455	$52.46	$52.45	$52.50
Purchase #7	$16.76	12.496%	$18.8543	$18.85	$18.85	$18.90
7 purchase totals =	$782.99		$861.1303	$861.13	$861.10	$861.10