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	$163.57	10.105%	$180.0987	$180.10	$180.10	$180.10
Purchase #2	$105.78	6.328%	$112.4738	$112.47	$112.45	$112.50
Purchase #3	$25.66	5.384%	$27.0415	$27.04	$27.05	$27.00
Purchase #4	$85.78	4.783%	$89.8829	$89.88	$89.90	$89.90
Purchase #5	$153.98	4.423%	$160.7905	$160.79	$160.80	$160.80
Purchase #6	$206.75	4.711%	$216.49	$216.49	$216.50	$216.50
Purchase #7	$139.71	5.507%	$147.4038	$147.40	$147.40	$147.40
7 purchase totals =	$881.23		$934.1812	$934.17	$934.20	$934.20