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	$71.85	3.536%	$74.3906	$74.39	$74.40	$74.40
Purchase #2	$66.30	7.856%	$71.5085	$71.51	$71.50	$71.50
Purchase #3	$70.68	12.503%	$79.5171	$79.52	$79.50	$79.50
Purchase #4	$162.89	3.199%	$168.1009	$168.10	$168.10	$168.10
Purchase #5	$43.77	9.439%	$47.9015	$47.90	$47.90	$47.90
Purchase #6	$112.30	3.750%	$116.5113	$116.51	$116.50	$116.50
Purchase #7	$59.70	5.740%	$63.1268	$63.13	$63.15	$63.10
7 purchase totals =	$587.49		$621.0567	$621.06	$621.05	$621.00