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	$82.29	9.702%	$90.2738	$90.27	$90.25	$90.30
Purchase #2	$24.30	10.211%	$26.7813	$26.78	$26.80	$26.80
Purchase #3	$132.54	7.553%	$142.5507	$142.55	$142.55	$142.60
Purchase #4	$69.65	13.322%	$78.9288	$78.93	$78.95	$78.90
Purchase #5	$150.83	9.243%	$164.7712	$164.77	$164.75	$164.80
Purchase #6	$193.67	13.716%	$220.2338	$220.23	$220.25	$220.20
Purchase #7	$80.74	4.462%	$84.3426	$84.34	$84.35	$84.30
7 purchase totals =	$734.02		$807.8822	$807.87	$807.90	$807.90