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	$29.73	6.625%	$31.6996	$31.70	$31.70	$31.70
Purchase #2	$133.37	5.609%	$140.8507	$140.85	$140.85	$140.90
Purchase #3	$131.64	4.548%	$137.627	$137.63	$137.65	$137.60
Purchase #4	$61.46	10.123%	$67.6816	$67.68	$67.70	$67.70
Purchase #5	$149.88	9.746%	$164.4873	$164.49	$164.50	$164.50
Purchase #6	$90.55	10.687%	$100.2271	$100.23	$100.25	$100.20
Purchase #7	$234.28	11.573%	$261.3932	$261.39	$261.40	$261.40
7 purchase totals =	$830.91		$903.9665	$903.97	$904.05	$904.00