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	$17.61	12.754%	$19.856	$19.86	$19.85	$19.90
Purchase #2	$203.76	5.724%	$215.4232	$215.42	$215.40	$215.40
Purchase #3	$125.40	5.182%	$131.8982	$131.90	$131.90	$131.90
Purchase #4	$131.56	6.121%	$139.6128	$139.61	$139.60	$139.60
Purchase #5	$130.54	9.270%	$142.6411	$142.64	$142.65	$142.60
Purchase #6	$179.46	5.690%	$189.6713	$189.67	$189.65	$189.70
Purchase #7	$10.91	10.333%	$12.0373	$12.04	$12.05	$12.00
7 purchase totals =	$799.24		$851.1399	$851.14	$851.10	$851.10