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	$18.81	3.178%	$19.4078	$19.41	$19.40	$19.40
Purchase #2	$248.78	12.677%	$280.3178	$280.32	$280.30	$280.30
Purchase #3	$101.63	12.566%	$114.4008	$114.40	$114.40	$114.40
Purchase #4	$24.75	13.260%	$28.0319	$28.03	$28.05	$28.00
Purchase #5	$41.31	6.219%	$43.8791	$43.88	$43.90	$43.90
Purchase #6	$144.51	5.128%	$151.9205	$151.92	$151.90	$151.90
Purchase #7	$179.43	4.270%	$187.0917	$187.09	$187.10	$187.10
7 purchase totals =	$759.22		$825.0496	$825.05	$825.05	$825.00