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	$108.85	10.158%	$119.907	$119.91	$119.90	$119.90
Purchase #2	$118.71	11.548%	$132.4186	$132.42	$132.40	$132.40
Purchase #3	$77.40	10.831%	$85.7832	$85.78	$85.80	$85.80
Purchase #4	$86.63	3.286%	$89.4767	$89.48	$89.50	$89.50
Purchase #5	$136.32	12.399%	$153.2223	$153.22	$153.20	$153.20
Purchase #6	$63.44	12.497%	$71.3681	$71.37	$71.35	$71.40
Purchase #7	$21.93	3.659%	$22.7324	$22.73	$22.75	$22.70
7 purchase totals =	$613.28		$674.9083	$674.91	$674.90	$674.90