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	$117.54	11.568%	$131.137	$131.14	$131.15	$131.10
Purchase #2	$101.31	11.763%	$113.2271	$113.23	$113.25	$113.20
Purchase #3	$172.35	3.365%	$178.1496	$178.15	$178.15	$178.10
Purchase #4	$50.85	6.206%	$54.0058	$54.01	$54.00	$54.00
Purchase #5	$93.70	7.680%	$100.8962	$100.90	$100.90	$100.90
Purchase #6	$142.96	12.792%	$161.2474	$161.25	$161.25	$161.20
Purchase #7	$89.87	12.379%	$100.995	$101.00	$101.00	$101.00
7 purchase totals =	$768.58		$839.6581	$839.68	$839.70	$839.50