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	$81.89	9.555%	$89.7146	$89.71	$89.70	$89.70
Purchase #2	$78.25	12.551%	$88.0712	$88.07	$88.05	$88.10
Purchase #3	$141.55	8.466%	$153.5336	$153.53	$153.55	$153.50
Purchase #4	$10.42	5.721%	$11.0161	$11.02	$11.00	$11.00
Purchase #5	$169.41	5.536%	$178.7885	$178.79	$178.80	$178.80
Purchase #6	$234.50	9.520%	$256.8244	$256.82	$256.80	$256.80
Purchase #7	$98.72	5.367%	$104.0183	$104.02	$104.00	$104.00
7 purchase totals =	$814.74		$881.9667	$881.96	$881.90	$881.90