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	$57.37	3.109%	$59.1536	$59.15	$59.15	$59.20
Purchase #2	$25.35	11.665%	$28.3071	$28.31	$28.30	$28.30
Purchase #3	$230.49	4.652%	$241.2124	$241.21	$241.20	$241.20
Purchase #4	$243.37	4.647%	$254.6794	$254.68	$254.70	$254.70
Purchase #5	$101.41	8.262%	$109.7885	$109.79	$109.80	$109.80
Purchase #6	$66.76	5.612%	$70.5066	$70.51	$70.50	$70.50
Purchase #7	$13.60	9.411%	$14.8799	$14.88	$14.90	$14.90
7 purchase totals =	$738.35		$778.5275	$778.53	$778.55	$778.60