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	$36.55	10.854%	$40.5171	$40.52	$40.50	$40.50
Purchase #2	$55.28	8.227%	$59.8279	$59.83	$59.85	$59.80
Purchase #3	$51.74	13.824%	$58.8925	$58.89	$58.90	$58.90
Purchase #4	$203.82	7.320%	$218.7396	$218.74	$218.75	$218.70
Purchase #5	$176.37	6.161%	$187.2362	$187.24	$187.25	$187.20
Purchase #6	$59.32	3.551%	$61.4265	$61.43	$61.45	$61.40
Purchase #7	$132.44	4.855%	$138.87	$138.87	$138.85	$138.90
7 purchase totals =	$715.52		$765.5098	$765.52	$765.55	$765.40