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	$125.81	9.343%	$137.5644	$137.56	$137.55	$137.60
Purchase #2	$116.60	10.717%	$129.096	$129.10	$129.10	$129.10
Purchase #3	$51.47	9.586%	$56.4039	$56.40	$56.40	$56.40
Purchase #4	$49.72	12.700%	$56.0344	$56.03	$56.05	$56.00
Purchase #5	$118.96	10.406%	$131.339	$131.34	$131.35	$131.30
Purchase #6	$98.26	7.368%	$105.4998	$105.50	$105.50	$105.50
Purchase #7	$44.97	5.726%	$47.545	$47.55	$47.55	$47.50
7 purchase totals =	$605.79		$663.4825	$663.48	$663.50	$663.40