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	$9.39	9.586%	$10.2901	$10.29	$10.30	$10.30
Purchase #2	$78.25	5.866%	$82.8401	$82.84	$82.85	$82.80
Purchase #3	$47.73	6.447%	$50.8072	$50.81	$50.80	$50.80
Purchase #4	$214.32	7.236%	$229.8282	$229.83	$229.85	$229.80
Purchase #5	$130.36	7.156%	$139.6886	$139.69	$139.70	$139.70
Purchase #6	$102.94	8.132%	$111.3111	$111.31	$111.30	$111.30
Purchase #7	$248.67	10.539%	$274.8773	$274.88	$274.90	$274.90
7 purchase totals =	$831.66		$899.6426	$899.65	$899.70	$899.60