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	$110.74	11.269%	$123.2193	$123.22	$123.20	$123.20
Purchase #2	$124.84	12.102%	$139.9481	$139.95	$139.95	$139.90
Purchase #3	$235.27	8.338%	$254.8868	$254.89	$254.90	$254.90
Purchase #4	$236.55	12.659%	$266.4949	$266.49	$266.50	$266.50
Purchase #5	$45.58	11.110%	$50.6439	$50.64	$50.65	$50.60
Purchase #6	$62.83	10.423%	$69.3788	$69.38	$69.40	$69.40
Purchase #7	$186.61	13.314%	$211.4553	$211.46	$211.45	$211.50
7 purchase totals =	$1,002.42		$1,116.0271	$1,116.03	$1,116.05	$1,116.00