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	$37.29	7.696%	$40.1598	$40.16	$40.15	$40.20
Purchase #2	$131.65	6.477%	$140.177	$140.18	$140.20	$140.20
Purchase #3	$37.58	7.189%	$40.2816	$40.28	$40.30	$40.30
Purchase #4	$38.35	12.573%	$43.1717	$43.17	$43.15	$43.20
Purchase #5	$40.31	10.644%	$44.6006	$44.60	$44.60	$44.60
Purchase #6	$109.59	10.727%	$121.3457	$121.35	$121.35	$121.30
Purchase #7	$93.28	3.148%	$96.2165	$96.22	$96.20	$96.20
7 purchase totals =	$488.05		$525.9529	$525.96	$525.95	$526.00