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	$16.47	6.239%	$17.4976	$17.50	$17.50	$17.50
Purchase #2	$217.72	3.451%	$225.2335	$225.23	$225.25	$225.20
Purchase #3	$141.53	9.123%	$154.4418	$154.44	$154.45	$154.40
Purchase #4	$197.46	13.132%	$223.3904	$223.39	$223.40	$223.40
Purchase #5	$242.78	5.512%	$256.162	$256.16	$256.15	$256.20
Purchase #6	$176.43	13.835%	$200.8391	$200.84	$200.85	$200.80
Purchase #7	$30.37	3.120%	$31.3175	$31.32	$31.30	$31.30
7 purchase totals =	$1,022.76		$1,108.8819	$1,108.88	$1,108.90	$1,108.80