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	$22.52	7.811%	$24.279	$24.28	$24.30	$24.30
Purchase #2	$72.52	13.442%	$82.2681	$82.27	$82.25	$82.30
Purchase #3	$19.52	3.311%	$20.1663	$20.17	$20.15	$20.20
Purchase #4	$162.26	11.242%	$180.5013	$180.50	$180.50	$180.50
Purchase #5	$70.59	11.220%	$78.5102	$78.51	$78.50	$78.50
Purchase #6	$71.31	3.241%	$73.6212	$73.62	$73.60	$73.60
Purchase #7	$230.86	12.277%	$259.2027	$259.20	$259.20	$259.20
7 purchase totals =	$649.58		$718.5488	$718.55	$718.50	$718.60