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	$59.26	11.230%	$65.9149	$65.91	$65.90	$65.90
Purchase #2	$144.25	9.459%	$157.8946	$157.89	$157.90	$157.90
Purchase #3	$249.97	6.316%	$265.7581	$265.76	$265.75	$265.80
Purchase #4	$48.72	8.286%	$52.7569	$52.76	$52.75	$52.80
Purchase #5	$107.38	5.133%	$112.8918	$112.89	$112.90	$112.90
Purchase #6	$71.66	12.638%	$80.7164	$80.72	$80.70	$80.70
Purchase #7	$231.46	5.371%	$243.8917	$243.89	$243.90	$243.90
7 purchase totals =	$912.70		$979.8244	$979.82	$979.80	$979.90