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	$240.78	7.863%	$259.7125	$259.71	$259.70	$259.70
Purchase #2	$55.65	12.706%	$62.7209	$62.72	$62.70	$62.70
Purchase #3	$152.57	5.292%	$160.644	$160.64	$160.65	$160.60
Purchase #4	$192.41	6.295%	$204.5222	$204.52	$204.50	$204.50
Purchase #5	$98.61	9.681%	$108.1564	$108.16	$108.15	$108.20
Purchase #6	$78.50	13.599%	$89.1752	$89.18	$89.20	$89.20
Purchase #7	$146.29	6.492%	$155.7871	$155.79	$155.80	$155.80
7 purchase totals =	$964.81		$1,040.7183	$1,040.72	$1,040.70	$1,040.70