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	$122.33	13.168%	$138.4384	$138.44	$138.45	$138.40
Purchase #2	$148.50	6.324%	$157.8911	$157.89	$157.90	$157.90
Purchase #3	$119.91	6.184%	$127.3252	$127.33	$127.35	$127.30
Purchase #4	$101.35	10.812%	$112.308	$112.31	$112.30	$112.30
Purchase #5	$52.81	12.702%	$59.5179	$59.52	$59.50	$59.50
Purchase #6	$8.91	10.415%	$9.838	$9.84	$9.85	$9.80
Purchase #7	$52.89	9.436%	$57.8807	$57.88	$57.90	$57.90
7 purchase totals =	$606.70		$663.1993	$663.21	$663.25	$663.10