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	$37.77	10.873%	$41.8767	$41.88	$41.90	$41.90
Purchase #2	$55.50	9.571%	$60.8119	$60.81	$60.80	$60.80
Purchase #3	$41.41	8.550%	$44.9506	$44.95	$44.95	$45.00
Purchase #4	$189.94	4.527%	$198.5386	$198.54	$198.55	$198.50
Purchase #5	$65.42	10.382%	$72.2119	$72.21	$72.20	$72.20
Purchase #6	$127.86	11.370%	$142.3977	$142.40	$142.40	$142.40
Purchase #7	$28.79	9.720%	$31.5884	$31.59	$31.60	$31.60
7 purchase totals =	$546.69		$592.3758	$592.38	$592.40	$592.40