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	$45.69	4.805%	$47.8854	$47.89	$47.90	$47.90
Purchase #2	$164.64	7.372%	$176.7773	$176.78	$176.80	$176.80
Purchase #3	$11.89	3.773%	$12.3386	$12.34	$12.35	$12.30
Purchase #4	$54.65	8.381%	$59.2302	$59.23	$59.25	$59.20
Purchase #5	$65.44	3.749%	$67.8933	$67.89	$67.90	$67.90
Purchase #6	$134.37	9.822%	$147.5678	$147.57	$147.55	$147.60
Purchase #7	$94.97	10.499%	$104.9409	$104.94	$104.95	$104.90
7 purchase totals =	$571.65		$616.6335	$616.64	$616.70	$616.60