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	$127.73	11.367%	$142.2491	$142.25	$142.25	$142.20
Purchase #2	$80.78	11.360%	$89.9566	$89.96	$89.95	$90.00
Purchase #3	$12.60	8.365%	$13.654	$13.65	$13.65	$13.70
Purchase #4	$150.99	12.544%	$169.9302	$169.93	$169.95	$169.90
Purchase #5	$58.53	12.724%	$65.9774	$65.98	$66.00	$66.00
Purchase #6	$18.30	5.827%	$19.3663	$19.37	$19.35	$19.40
Purchase #7	$59.40	13.840%	$67.621	$67.62	$67.60	$67.60
7 purchase totals =	$508.33		$568.7546	$568.76	$568.75	$568.80