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	$50.39	11.108%	$55.9873	$55.99	$56.00	$56.00
Purchase #2	$189.54	3.662%	$196.481	$196.48	$196.50	$196.50
Purchase #3	$82.94	4.693%	$86.8324	$86.83	$86.85	$86.80
Purchase #4	$195.91	10.115%	$215.7263	$215.73	$215.75	$215.70
Purchase #5	$124.39	9.143%	$135.763	$135.76	$135.75	$135.80
Purchase #6	$49.41	6.233%	$52.4897	$52.49	$52.50	$52.50
Purchase #7	$223.82	7.778%	$241.2287	$241.23	$241.25	$241.20
7 purchase totals =	$916.40		$984.5084	$984.51	$984.60	$984.50