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	$36.70	9.549%	$40.2045	$40.20	$40.20	$40.20
Purchase #2	$195.47	6.157%	$207.5051	$207.51	$207.50	$207.50
Purchase #3	$78.78	13.513%	$89.4255	$89.43	$89.45	$89.40
Purchase #4	$166.72	4.695%	$174.5475	$174.55	$174.55	$174.50
Purchase #5	$142.25	13.151%	$160.9573	$160.96	$160.95	$161.00
Purchase #6	$117.71	11.834%	$131.6398	$131.64	$131.65	$131.60
Purchase #7	$25.34	13.458%	$28.7503	$28.75	$28.75	$28.80
7 purchase totals =	$762.97		$833.0300	$833.04	$833.05	$833.00