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	$229.78	7.866%	$247.8545	$247.85	$247.85	$247.90
Purchase #2	$184.96	9.156%	$201.8949	$201.89	$201.90	$201.90
Purchase #3	$227.45	4.858%	$238.4995	$238.50	$238.50	$238.50
Purchase #4	$190.48	10.723%	$210.9052	$210.91	$210.90	$210.90
Purchase #5	$125.83	7.186%	$134.8721	$134.87	$134.85	$134.90
Purchase #6	$235.65	12.686%	$265.5446	$265.54	$265.55	$265.50
Purchase #7	$38.32	10.444%	$42.3221	$42.32	$42.30	$42.30
7 purchase totals =	$1,232.47		$1,341.8929	$1,341.88	$1,341.85	$1,341.90