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	$75.36	10.582%	$83.3346	$83.33	$83.35	$83.30
Purchase #2	$34.52	11.488%	$38.4857	$38.49	$38.50	$38.50
Purchase #3	$114.94	10.379%	$126.8696	$126.87	$126.85	$126.90
Purchase #4	$103.83	7.447%	$111.5622	$111.56	$111.55	$111.60
Purchase #5	$205.64	8.796%	$223.7281	$223.73	$223.75	$223.70
Purchase #6	$170.83	6.638%	$182.1697	$182.17	$182.15	$182.20
Purchase #7	$230.77	4.498%	$241.15	$241.15	$241.15	$241.20
7 purchase totals =	$935.89		$1,007.2999	$1,007.30	$1,007.30	$1,007.40