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	$44.30	13.858%	$50.4391	$50.44	$50.45	$50.40
Purchase #2	$117.63	12.547%	$132.389	$132.39	$132.40	$132.40
Purchase #3	$51.69	4.801%	$54.1716	$54.17	$54.15	$54.20
Purchase #4	$119.44	13.294%	$135.3184	$135.32	$135.30	$135.30
Purchase #5	$210.85	4.194%	$219.693	$219.69	$219.70	$219.70
Purchase #6	$171.76	9.154%	$187.4829	$187.48	$187.50	$187.50
Purchase #7	$85.89	5.249%	$90.3984	$90.40	$90.40	$90.40
7 purchase totals =	$801.56		$869.8924	$869.89	$869.90	$869.90