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	$23.28	4.149%	$24.2459	$24.25	$24.25	$24.20
Purchase #2	$127.39	3.684%	$132.083	$132.08	$132.10	$132.10
Purchase #3	$202.52	13.341%	$229.5382	$229.54	$229.55	$229.50
Purchase #4	$146.43	12.576%	$164.845	$164.85	$164.85	$164.80
Purchase #5	$246.61	4.873%	$258.6273	$258.63	$258.65	$258.60
Purchase #6	$49.34	3.279%	$50.9579	$50.96	$50.95	$51.00
Purchase #7	$132.37	12.248%	$148.5827	$148.58	$148.60	$148.60
7 purchase totals =	$927.94		$1,008.8800	$1,008.89	$1,008.95	$1,008.80