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	$216.49	10.788%	$239.8449	$239.84	$239.85	$239.80
Purchase #2	$193.81	3.629%	$200.8434	$200.84	$200.85	$200.80
Purchase #3	$158.79	4.161%	$165.3973	$165.40	$165.40	$165.40
Purchase #4	$149.87	11.821%	$167.5861	$167.59	$167.60	$167.60
Purchase #5	$80.56	11.535%	$89.8526	$89.85	$89.85	$89.90
Purchase #6	$93.89	10.798%	$104.0282	$104.03	$104.05	$104.00
Purchase #7	$7.81	12.427%	$8.7805	$8.78	$8.80	$8.80
7 purchase totals =	$901.22		$976.3330	$976.33	$976.40	$976.30