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	$88.79	13.299%	$100.5982	$100.60	$100.60	$100.60
Purchase #2	$47.87	8.544%	$51.96	$51.96	$51.95	$52.00
Purchase #3	$219.50	10.458%	$242.4553	$242.46	$242.45	$242.50
Purchase #4	$109.61	4.403%	$114.4361	$114.44	$114.45	$114.40
Purchase #5	$81.69	12.264%	$91.7085	$91.71	$91.70	$91.70
Purchase #6	$201.90	5.589%	$213.1842	$213.18	$213.20	$213.20
Purchase #7	$51.40	6.342%	$54.6598	$54.66	$54.65	$54.70
7 purchase totals =	$800.76		$869.0021	$869.01	$869.00	$869.10