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	$34.70	12.224%	$38.9417	$38.94	$38.95	$38.90
Purchase #2	$152.34	10.127%	$167.7675	$167.77	$167.75	$167.80
Purchase #3	$68.25	9.733%	$74.8928	$74.89	$74.90	$74.90
Purchase #4	$156.71	3.788%	$162.6462	$162.65	$162.65	$162.60
Purchase #5	$122.35	6.136%	$129.8574	$129.86	$129.85	$129.90
Purchase #6	$155.78	10.746%	$172.5201	$172.52	$172.50	$172.50
Purchase #7	$99.54	3.791%	$103.3136	$103.31	$103.30	$103.30
7 purchase totals =	$789.67		$849.9393	$849.94	$849.90	$849.90