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	$38.42	9.763%	$42.1709	$42.17	$42.15	$42.20
Purchase #2	$36.89	4.438%	$38.5272	$38.53	$38.55	$38.50
Purchase #3	$147.74	4.558%	$154.474	$154.47	$154.45	$154.50
Purchase #4	$250.30	10.302%	$276.0859	$276.09	$276.10	$276.10
Purchase #5	$239.69	7.185%	$256.9117	$256.91	$256.90	$256.90
Purchase #6	$14.61	6.220%	$15.5187	$15.52	$15.50	$15.50
Purchase #7	$132.49	10.577%	$146.5035	$146.50	$146.50	$146.50
7 purchase totals =	$860.14		$930.1919	$930.19	$930.15	$930.20