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	$105.97	13.792%	$120.5854	$120.59	$120.60	$120.60
Purchase #2	$10.97	9.380%	$11.999	$12.00	$12.00	$12.00
Purchase #3	$48.75	9.166%	$53.2184	$53.22	$53.20	$53.20
Purchase #4	$191.75	11.202%	$213.2298	$213.23	$213.25	$213.20
Purchase #5	$193.53	11.167%	$215.1415	$215.14	$215.15	$215.10
Purchase #6	$207.57	4.328%	$216.5536	$216.55	$216.55	$216.60
Purchase #7	$74.61	4.754%	$78.157	$78.16	$78.15	$78.20
7 purchase totals =	$833.15		$908.8847	$908.89	$908.90	$908.90