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	$159.39	8.230%	$172.5078	$172.51	$172.50	$172.50
Purchase #2	$142.64	12.490%	$160.4557	$160.46	$160.45	$160.50
Purchase #3	$103.28	6.344%	$109.8321	$109.83	$109.85	$109.80
Purchase #4	$244.90	3.754%	$254.0935	$254.09	$254.10	$254.10
Purchase #5	$54.55	5.667%	$57.6413	$57.64	$57.65	$57.60
Purchase #6	$168.48	5.380%	$177.5442	$177.54	$177.55	$177.50
Purchase #7	$238.96	3.295%	$246.8337	$246.83	$246.85	$246.80
7 purchase totals =	$1,112.20		$1,178.9083	$1,178.90	$1,178.95	$1,178.80