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	$36.93	9.763%	$40.5355	$40.54	$40.55	$40.50
Purchase #2	$74.81	4.213%	$77.9617	$77.96	$77.95	$78.00
Purchase #3	$155.70	13.443%	$176.6308	$176.63	$176.65	$176.60
Purchase #4	$10.50	13.228%	$11.8889	$11.89	$11.90	$11.90
Purchase #5	$162.99	3.250%	$168.2872	$168.29	$168.30	$168.30
Purchase #6	$140.94	10.741%	$156.0784	$156.08	$156.10	$156.10
Purchase #7	$30.51	8.561%	$33.122	$33.12	$33.10	$33.10
7 purchase totals =	$612.38		$664.5045	$664.51	$664.55	$664.50