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	$41.44	7.297%	$44.4639	$44.46	$44.45	$44.50
Purchase #2	$37.40	8.330%	$40.5154	$40.52	$40.50	$40.50
Purchase #3	$105.42	13.123%	$119.2543	$119.25	$119.25	$119.30
Purchase #4	$246.66	13.691%	$280.4302	$280.43	$280.45	$280.40
Purchase #5	$92.90	6.122%	$98.5873	$98.59	$98.60	$98.60
Purchase #6	$40.79	7.212%	$43.7318	$43.73	$43.75	$43.70
Purchase #7	$15.68	4.169%	$16.3337	$16.33	$16.35	$16.30
7 purchase totals =	$580.29		$643.3166	$643.31	$643.35	$643.30