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	$16.53	12.516%	$18.5989	$18.60	$18.60	$18.60
Purchase #2	$78.89	4.702%	$82.5994	$82.60	$82.60	$82.60
Purchase #3	$228.52	11.373%	$254.5096	$254.51	$254.50	$254.50
Purchase #4	$243.48	6.531%	$259.3817	$259.38	$259.40	$259.40
Purchase #5	$168.40	7.341%	$180.7622	$180.76	$180.75	$180.80
Purchase #6	$89.76	13.650%	$102.0122	$102.01	$102.00	$102.00
Purchase #7	$140.42	3.158%	$144.8545	$144.85	$144.85	$144.90
7 purchase totals =	$966.00		$1,042.7185	$1,042.71	$1,042.70	$1,042.80