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	$148.63	12.848%	$167.726	$167.73	$167.75	$167.70
Purchase #2	$119.37	3.461%	$123.5014	$123.50	$123.50	$123.50
Purchase #3	$47.86	9.712%	$52.5082	$52.51	$52.50	$52.50
Purchase #4	$58.26	10.591%	$64.4303	$64.43	$64.45	$64.40
Purchase #5	$104.53	7.564%	$112.4366	$112.44	$112.45	$112.40
Purchase #6	$6.47	13.663%	$7.354	$7.35	$7.35	$7.40
Purchase #7	$132.33	6.505%	$140.9381	$140.94	$140.95	$140.90
7 purchase totals =	$617.45		$668.8946	$668.90	$668.95	$668.80