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	$120.46	8.490%	$130.6871	$130.69	$130.70	$130.70
Purchase #2	$68.84	3.277%	$71.0959	$71.10	$71.10	$71.10
Purchase #3	$12.38	11.479%	$13.8011	$13.80	$13.80	$13.80
Purchase #4	$127.43	12.247%	$143.0364	$143.04	$143.05	$143.00
Purchase #5	$39.67	6.515%	$42.2545	$42.25	$42.25	$42.30
Purchase #6	$157.57	4.339%	$164.407	$164.41	$164.40	$164.40
Purchase #7	$25.35	11.426%	$28.2465	$28.25	$28.25	$28.20
7 purchase totals =	$551.70		$593.5285	$593.54	$593.55	$593.50