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	$34.72	13.708%	$39.4794	$39.48	$39.50	$39.50
Purchase #2	$244.68	7.774%	$263.7014	$263.70	$263.70	$263.70
Purchase #3	$136.31	10.140%	$150.1318	$150.13	$150.15	$150.10
Purchase #4	$192.73	12.281%	$216.3992	$216.40	$216.40	$216.40
Purchase #5	$238.81	8.602%	$259.3524	$259.35	$259.35	$259.40
Purchase #6	$40.56	13.352%	$45.9756	$45.98	$46.00	$46.00
Purchase #7	$34.62	11.178%	$38.4898	$38.49	$38.50	$38.50
7 purchase totals =	$922.43		$1,013.5296	$1,013.53	$1,013.60	$1,013.60