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	$36.37	10.703%	$40.2627	$40.26	$40.25	$40.30
Purchase #2	$244.67	5.285%	$257.6008	$257.60	$257.60	$257.60
Purchase #3	$105.48	11.729%	$117.8517	$117.85	$117.85	$117.90
Purchase #4	$195.99	11.470%	$218.4701	$218.47	$218.45	$218.50
Purchase #5	$131.39	7.733%	$141.5504	$141.55	$141.55	$141.60
Purchase #6	$32.77	3.809%	$34.0182	$34.02	$34.00	$34.00
Purchase #7	$37.55	13.408%	$42.5847	$42.58	$42.60	$42.60
7 purchase totals =	$784.22		$852.3386	$852.33	$852.30	$852.50