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	$40.45	4.832%	$42.4045	$42.40	$42.40	$42.40
Purchase #2	$59.89	13.740%	$68.1189	$68.12	$68.10	$68.10
Purchase #3	$239.93	4.130%	$249.8391	$249.84	$249.85	$249.80
Purchase #4	$182.28	12.638%	$205.3165	$205.32	$205.30	$205.30
Purchase #5	$90.80	7.429%	$97.5455	$97.55	$97.55	$97.50
Purchase #6	$159.88	5.239%	$168.2561	$168.26	$168.25	$168.30
Purchase #7	$64.79	4.836%	$67.9232	$67.92	$67.90	$67.90
7 purchase totals =	$838.02		$899.4038	$899.41	$899.35	$899.30