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	$99.95	12.711%	$112.6546	$112.65	$112.65	$112.70
Purchase #2	$53.65	10.847%	$59.4694	$59.47	$59.45	$59.50
Purchase #3	$7.61	6.508%	$8.1053	$8.11	$8.10	$8.10
Purchase #4	$38.28	12.384%	$43.0206	$43.02	$43.00	$43.00
Purchase #5	$102.91	6.505%	$109.6043	$109.60	$109.60	$109.60
Purchase #6	$34.88	12.297%	$39.1692	$39.17	$39.15	$39.20
Purchase #7	$189.88	9.328%	$207.592	$207.59	$207.60	$207.60
7 purchase totals =	$527.16		$579.6154	$579.61	$579.55	$579.70