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	$43.87	11.651%	$48.9813	$48.98	$49.00	$49.00
Purchase #2	$41.40	8.379%	$44.8689	$44.87	$44.85	$44.90
Purchase #3	$66.91	6.801%	$71.4605	$71.46	$71.45	$71.50
Purchase #4	$247.33	13.355%	$280.3609	$280.36	$280.35	$280.40
Purchase #5	$190.86	5.248%	$200.8763	$200.88	$200.90	$200.90
Purchase #6	$94.95	6.619%	$101.2347	$101.23	$101.25	$101.20
Purchase #7	$18.80	9.486%	$20.5834	$20.58	$20.60	$20.60
7 purchase totals =	$704.12		$768.3660	$768.36	$768.40	$768.50