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	$18.56	10.389%	$20.4882	$20.49	$20.50	$20.50
Purchase #2	$52.81	9.654%	$57.9083	$57.91	$57.90	$57.90
Purchase #3	$191.80	12.248%	$215.2917	$215.29	$215.30	$215.30
Purchase #4	$13.25	9.141%	$14.4612	$14.46	$14.45	$14.50
Purchase #5	$90.37	5.490%	$95.3313	$95.33	$95.35	$95.30
Purchase #6	$147.91	13.561%	$167.9681	$167.97	$167.95	$168.00
Purchase #7	$116.32	10.410%	$128.4289	$128.43	$128.45	$128.40
7 purchase totals =	$631.02		$699.8777	$699.88	$699.90	$699.90