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	$58.32	6.148%	$61.9055	$61.91	$61.90	$61.90
Purchase #2	$7.43	8.123%	$8.0335	$8.03	$8.05	$8.00
Purchase #3	$135.25	8.592%	$146.8707	$146.87	$146.85	$146.90
Purchase #4	$121.68	13.720%	$138.3745	$138.37	$138.35	$138.40
Purchase #5	$72.88	13.659%	$82.8347	$82.83	$82.85	$82.80
Purchase #6	$86.92	9.837%	$95.4703	$95.47	$95.45	$95.50
Purchase #7	$101.80	7.211%	$109.1408	$109.14	$109.15	$109.10
7 purchase totals =	$584.28		$642.6300	$642.62	$642.60	$642.60