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	$19.60	8.246%	$21.2162	$21.22	$21.20	$21.20
Purchase #2	$196.46	5.318%	$206.9077	$206.91	$206.90	$206.90
Purchase #3	$150.41	5.210%	$158.2464	$158.25	$158.25	$158.20
Purchase #4	$43.57	5.271%	$45.8666	$45.87	$45.85	$45.90
Purchase #5	$93.96	12.238%	$105.4588	$105.46	$105.45	$105.50
Purchase #6	$160.47	12.372%	$180.3233	$180.32	$180.30	$180.30
Purchase #7	$85.30	12.628%	$96.0717	$96.07	$96.05	$96.10
7 purchase totals =	$749.77		$814.0907	$814.10	$814.00	$814.10