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	$162.67	10.584%	$179.887	$179.89	$179.90	$179.90
Purchase #2	$28.28	7.704%	$30.4587	$30.46	$30.45	$30.50
Purchase #3	$36.87	5.423%	$38.8695	$38.87	$38.85	$38.90
Purchase #4	$161.88	9.284%	$176.9089	$176.91	$176.90	$176.90
Purchase #5	$165.71	9.479%	$181.4177	$181.42	$181.40	$181.40
Purchase #6	$178.60	7.430%	$191.87	$191.87	$191.85	$191.90
Purchase #7	$171.44	5.649%	$181.1246	$181.12	$181.10	$181.10
7 purchase totals =	$905.45		$980.5364	$980.54	$980.45	$980.60