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	$124.89	11.510%	$139.2648	$139.26	$139.25	$139.30
Purchase #2	$123.79	3.386%	$127.9815	$127.98	$128.00	$128.00
Purchase #3	$171.78	7.205%	$184.1567	$184.16	$184.15	$184.20
Purchase #4	$250.45	6.182%	$265.9328	$265.93	$265.95	$265.90
Purchase #5	$19.71	11.337%	$21.9445	$21.94	$21.95	$21.90
Purchase #6	$133.96	5.569%	$141.4202	$141.42	$141.40	$141.40
Purchase #7	$167.73	12.335%	$188.4195	$188.42	$188.40	$188.40
7 purchase totals =	$992.31		$1,069.1200	$1,069.11	$1,069.10	$1,069.10