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	$178.37	4.220%	$185.8972	$185.90	$185.90	$185.90
Purchase #2	$51.66	6.701%	$55.1217	$55.12	$55.10	$55.10
Purchase #3	$98.87	4.709%	$103.5258	$103.53	$103.55	$103.50
Purchase #4	$158.99	12.850%	$179.4202	$179.42	$179.40	$179.40
Purchase #5	$160.54	8.161%	$173.6417	$173.64	$173.65	$173.60
Purchase #6	$249.31	12.366%	$280.1397	$280.14	$280.15	$280.10
Purchase #7	$92.82	11.704%	$103.6837	$103.68	$103.70	$103.70
7 purchase totals =	$990.56		$1,081.4300	$1,081.43	$1,081.45	$1,081.30