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	$49.99	11.404%	$55.6909	$55.69	$55.70	$55.70
Purchase #2	$172.34	8.788%	$187.4852	$187.49	$187.50	$187.50
Purchase #3	$181.55	6.111%	$192.6445	$192.64	$192.65	$192.60
Purchase #4	$83.82	11.691%	$93.6194	$93.62	$93.60	$93.60
Purchase #5	$91.25	13.572%	$103.6345	$103.63	$103.65	$103.60
Purchase #6	$104.64	6.120%	$111.044	$111.04	$111.05	$111.00
Purchase #7	$14.72	5.531%	$15.5342	$15.53	$15.55	$15.50
7 purchase totals =	$698.31		$759.6527	$759.64	$759.70	$759.50