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	$137.61	13.152%	$155.7085	$155.71	$155.70	$155.70
Purchase #2	$81.55	9.847%	$89.5802	$89.58	$89.60	$89.60
Purchase #3	$226.64	13.427%	$257.071	$257.07	$257.05	$257.10
Purchase #4	$56.38	13.321%	$63.8904	$63.89	$63.90	$63.90
Purchase #5	$113.51	13.181%	$128.4718	$128.47	$128.45	$128.50
Purchase #6	$179.41	11.141%	$199.3981	$199.40	$199.40	$199.40
Purchase #7	$80.29	6.416%	$85.4414	$85.44	$85.45	$85.40
7 purchase totals =	$875.39		$979.5614	$979.56	$979.55	$979.60