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	$13.42	13.455%	$15.2257	$15.23	$15.25	$15.20
Purchase #2	$150.32	8.104%	$162.5019	$162.50	$162.50	$162.50
Purchase #3	$234.93	12.280%	$263.7794	$263.78	$263.80	$263.80
Purchase #4	$60.83	11.542%	$67.851	$67.85	$67.85	$67.90
Purchase #5	$67.59	7.165%	$72.4328	$72.43	$72.45	$72.40
Purchase #6	$78.26	11.362%	$87.1519	$87.15	$87.15	$87.20
Purchase #7	$14.30	10.788%	$15.8427	$15.84	$15.85	$15.80
7 purchase totals =	$619.65		$684.7854	$684.78	$684.85	$684.80