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	$104.55	6.499%	$111.3447	$111.34	$111.35	$111.30
Purchase #2	$22.84	12.542%	$25.7046	$25.70	$25.70	$25.70
Purchase #3	$241.88	7.378%	$259.7259	$259.73	$259.75	$259.70
Purchase #4	$43.50	5.357%	$45.8303	$45.83	$45.85	$45.80
Purchase #5	$177.91	10.270%	$196.1814	$196.18	$196.20	$196.20
Purchase #6	$215.42	11.498%	$240.189	$240.19	$240.20	$240.20
Purchase #7	$249.33	12.476%	$280.4364	$280.44	$280.45	$280.40
7 purchase totals =	$1,055.43		$1,159.4123	$1,159.41	$1,159.50	$1,159.30