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	$54.44	5.779%	$57.5861	$57.59	$57.60	$57.60
Purchase #2	$132.48	9.210%	$144.6814	$144.68	$144.70	$144.70
Purchase #3	$198.41	12.769%	$223.745	$223.75	$223.75	$223.70
Purchase #4	$127.77	3.215%	$131.8778	$131.88	$131.90	$131.90
Purchase #5	$194.59	5.454%	$205.2029	$205.20	$205.20	$205.20
Purchase #6	$102.88	12.228%	$115.4602	$115.46	$115.45	$115.50
Purchase #7	$54.34	12.713%	$61.2482	$61.25	$61.25	$61.20
7 purchase totals =	$864.91		$939.8016	$939.81	$939.85	$939.80