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	$25.99	11.265%	$28.9178	$28.92	$28.90	$28.90
Purchase #2	$213.78	11.523%	$238.4139	$238.41	$238.40	$238.40
Purchase #3	$188.66	4.309%	$196.7894	$196.79	$196.80	$196.80
Purchase #4	$128.88	9.720%	$141.4071	$141.41	$141.40	$141.40
Purchase #5	$204.38	11.767%	$228.4294	$228.43	$228.45	$228.40
Purchase #6	$166.45	12.513%	$187.2779	$187.28	$187.30	$187.30
Purchase #7	$139.42	5.711%	$147.3823	$147.38	$147.40	$147.40
7 purchase totals =	$1,067.56		$1,168.6178	$1,168.62	$1,168.65	$1,168.60