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	$54.83	4.322%	$57.1998	$57.20	$57.20	$57.20
Purchase #2	$196.40	4.532%	$205.3008	$205.30	$205.30	$205.30
Purchase #3	$104.39	12.515%	$117.4544	$117.45	$117.45	$117.50
Purchase #4	$122.57	7.576%	$131.8559	$131.86	$131.85	$131.90
Purchase #5	$150.57	13.587%	$171.0279	$171.03	$171.05	$171.00
Purchase #6	$179.63	12.718%	$202.4753	$202.48	$202.50	$202.50
Purchase #7	$103.93	7.364%	$111.5834	$111.58	$111.60	$111.60
7 purchase totals =	$912.32		$996.8975	$996.90	$996.95	$997.00