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	$79.61	13.288%	$90.1886	$90.19	$90.20	$90.20
Purchase #2	$210.77	8.588%	$228.8709	$228.87	$228.85	$228.90
Purchase #3	$174.62	5.308%	$183.8888	$183.89	$183.90	$183.90
Purchase #4	$89.85	9.671%	$98.5394	$98.54	$98.55	$98.50
Purchase #5	$99.63	5.493%	$105.1027	$105.10	$105.10	$105.10
Purchase #6	$117.40	13.197%	$132.8933	$132.89	$132.90	$132.90
Purchase #7	$62.76	10.864%	$69.5782	$69.58	$69.60	$69.60
7 purchase totals =	$834.64		$909.0619	$909.06	$909.10	$909.10