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	$18.27	12.637%	$20.5788	$20.58	$20.60	$20.60
Purchase #2	$221.54	7.200%	$237.4909	$237.49	$237.50	$237.50
Purchase #3	$38.58	12.492%	$43.3994	$43.40	$43.40	$43.40
Purchase #4	$37.40	13.714%	$42.529	$42.53	$42.55	$42.50
Purchase #5	$247.83	13.261%	$280.6947	$280.69	$280.70	$280.70
Purchase #6	$238.41	8.365%	$258.353	$258.35	$258.35	$258.40
Purchase #7	$242.74	12.686%	$273.534	$273.53	$273.55	$273.50
7 purchase totals =	$1,044.77		$1,156.5798	$1,156.57	$1,156.65	$1,156.60